Energy Savings: Newsletter Challenge (08/01/08)

Well without any figures being given...

say the 19" CRTs consumed 100 Watts more than the 17" LCDs

That is 60 x 100 = 6kW of savings...

BUT - if the ambient temperature goes below 70*F then the savings are reduced as the heating would need to replace the 'lost' 6kW.

So there is no simple answer to this.

John.

I'm with you John, insufficient data. You would need an average year-round temperature, and short of knowing exactly how well the buildings insulated, at least a rough figure (preferably daily to compare) on how much cooling and heating was required and cross-reference that to the outside temperature again preferably a day by day comparison.
About 26 years ago I was involved with the building here in Southern California that had all their fluorescence lighting fixtures replace with new energy-efficient electronic ballast units, the boilers hadn't been used in years, in fact they were in disrepair and inoperative, and you guessed it they were screaming for heat the first cold day.

PS. There is a wildcard here I had a building that I remotely monitored, and I found even on are rarer thirtysomething degree mornings the building required cooling, heat load from personal computers was virtually nonexistent 26 years ago.

So there is no simple answer to this.

Indeed. The ambiguities just pile on on top of one another.

In most parts of the northeast US, the time-weighted average annual temperature is less than 70 degrees. In that case, the waste heat from the monitors is, on average, reducing the heating requirement.

But perhaps the building is heated by gas, in which case the dollar cost of heating-by-monitor would be higher than the dollar cost of heating with gas.

On the other hand, perhaps the people sitting near the monitors would get enough radiant heat from the monitors that the overall temperature of the building could be reduced, possibly making heat-by-monitor a good deal: better to heat just the people, rather than the whole building.

Are we nerds, or what??

Are we nerds, or what??

I'm mostly a 'What'

Surely the answer is...
If it's a fait accompli* then WTF does it matter.
If they haven't done it yet, then leave it as a scheduled replacement when monitors fail..why discard working stuff..the 'throw away ' society is a plague.
Unless of course they are donating them to a Worthy cause like the 'Make Bill Gates even more wealthy Foundation'

Del

*Isn't that a new Italian Car?

".why discard working stuff."

Fear of WEEE regulations?(Waste Electrical and Electronic Equipment)

All Eurozone is covered - Is there something similar in the States?

The lead (Pb) content of CRTs is of concern to the powers that be, and costs of disposal are set to rise to ridiculous levels. Most companies are replacing CRTs now, as end-of -life disposal for NEW items is now the problem of the SUPPLIER, so it sort of makes (financial) sense to switch to new products covered by the new legislation and turf the "old" ones while they can still cheaply go to landfill..... much more environmentally friendly????

But whose energy are we saving anyway?

Fear of WEEE regulations?

That makes NO sense...
We are frightened of waste regualtions ...so we'll waste some stuff...you are obviously in Management

I guess we are all nerds.

One other thing to consider is that productivity may be lower with a smaller screen. It doesn't take a lot of lowered productivity at perhaps $20/hr to $100/hr to negate any energy savings at perhaps $0.01/hr.

Most of the responses appear to be from engineer-types. This question should be asked of an accountant -- and the answer likely would be, "How much do you want the savings to be?" Because there are a number of factors that can be considered, and what an accountant chooses to include or exclude would affect the resulting 'savings' quite a bit. (As has already been alluded to by other posts.)

In addition to some of the factors that have already been suggested is the 'factor' of whether the company's MIS department requires that all monitors go into power-saving 'sleep' mode when no activity has occurred after, say, 10 minutes. A CRT in 'sleep' mode consumes less power than once displaying an MSWord document.

The accountant might also suggest waiting a year or so until LCD monitors using LED lighting are available, since LEDs are now available with better efficacy than fluorescent lamps. LEDs are being used in some home TV-LCDs and in special industrial monitors, and the PC monitor market will see them soon.

And if the company is really concerned about saving a few $$$, why not set the thermostat to 72F in the summer and 68F in the winter? And switch to a 4-day work week. Those two changes in company operation would likely save a lot more money than changing-out the monitors.

I wanted to give this a thumbs up, but apparently responses to 'off topic' are precluded.

Answer: Never

Reason: LCD monitors contain mercury. Any savings gained by reduced electrical usage will be overcome by legal fees required to defend against Al Gore's onslaught of legal suits.

It will be Company X vs. Man-Bear-Pig and it won't be pretty.

So do most of my fillings in my teeth but I am not to worried because it as a compond just like in the monitor!!

The mercury in the lamps is not in a safe compound

I don't know how long it would take to pay for the completely as there is listed no cost of the new LCD monitors or the local rate per kilowatt charged by the utility company. The biggest factor in length of time may be the use habits of the workers. With 60 monitors going switching to sleep mode when unattended. For unknown lengths of time.

But I do know that the energy savings will start paying for the new LCD monitors immediately.

But I do know that the energy savings will start paying for the new LCD monitors immediately.

How do you know that??

The building could be in a very cold area with high heating costs... So the loss of 6kW of waste heat from the old CRT monitors would need to be replaced by the heating working extra hard - and costing more?

There is just not enough information.... a bit like the school boy homework questions we get on here.

John.

hmmm,

Northeast US... Near Gulfstream huh? Is it possible our company is paying only for cooling ??

CRTs should be hot enough to feel like an oven. I'll take the 80% of energy converted to heat with CRT, and say heat of 5W LCD dissipates(i'm working for the director of company!).

A desktop CRT of 19" consumes 100-150W, averaged to 125W.

An LCD of 17" consumes 30-50W, averaged to 40W.

Our company consumes 85W-h less than that of CRTs, per hour. And the coolers operates less duration than that of CRTs exists. I'll take the energy counterpart of this offtime of coolers as 125*80% = 100W. (excellent! we found nonrounded round number, i'll not get also into account the efficiency of coolers etc...)

The total gain of power is 100+85-5=180W per monitor = 0,18 kW.

Say cost of electricity is 10 cent per kW-h, this yields 60*10*0,18 ≥ 1$ per hour for 60 monitors.

How much is a LCD of 17" nowadays? I'll throw it as 200$. Money that company spent is 12.000 $. Period to reclaim this money will be 12000 hours = 500 days.

Assuming this company is working so as 7/24, the 12.000 usd has been taken back after 16 months!

This is the director's decision, it does not seem worthwhile though.

Northeast is about New York or Boston at a guess feridun,

Gulf stream is much further south - near the gulf

Also your maths is assuming a great deal and flawed.

John.

Looking from Istanbul the distances are very little, trust me!

flaws.. Ah! How to find floors with basement falled down?

Best regards

f.h.

Yes they will save electricity but I just had a rude surprise on my LCD. Yesterday I came home from work and there is a blue vertical line down across the center of my screen. Seems that one of the blue column driver transistors fried on. The monitor is no more than 18 months old and of course works fine otherwise. My last monitor, a CRT lasted for 7 or so years and is still working fine where I donated it. I just wanted more real estate for CAD (1200x1600 LCD) but I guess I will have to look at life expectancy with my next purchase. Factor that into your calculations!

This must be that called bad chance!

What about the warranty my dear?

<What about the warranty my dear?>

Yes, it's under warranty, but the manufacturer is trying to get me to take a smaller screen in exchange. This looks interesting! I'm not out of the woods yet.

commercial logic!

They are the same wherever they are.

Unlucky Guest.

I've had my 17" LCD for over 5 ½ years working 6 hours a day and so far its never had a problem.

My last 17" CRT blew its line output transistor after only 2 years!

I guess its the luck of the draw...

John.

"...and there is a blue vertical line down across the center of my screen."

Otherwise referred to as a 'calibration mark'.

If your LCD is an older style TN LCD, in which the LCD is white in the off state and is driven black in the on state, then the blue line may simply be due to an unstuck flex connection at the edge of the LCD for that column of blue sub-pixels. You might be able to apply a slight squeeze and get it to re-connect.

Newer in-plane-switching or vertical-alignment LCDs are normally black, and are driven white in the on state. If the LCD is this type then you're probably right about it being a stuck-on transistor. Too bad.

This is unlikly the case as each pixel uses its own transistor they moved away from coloumn/row driving years ago ... more likely a dry joint as i have seen on many monitors... Also maybe just your video card try a different colour setting ie 32 bit colour to 16 bit colour you mind it is that !!!

I think what they save over the summer they'll lose in the winter, so they'll break even.

Mark

There will be savings, but probably not enough to pay for the LCD screens within their lifetimes. So it's clearly not a winner financially, unless there are other reasons for making the change.

In winter they will have to replace the saved heat using some other source; but, unless they use the crudest electrical heaters there will still be overall savings, as electricity is by far the most expensive source for daytime thermal power (electrically-driven heat pumps might be economical, but that is not what happens in a CRT or LCD display). So at least half of any direct electricity costs should be saved in the winter. The savings in summer will exceed the cost of the electricity saved directly by the change-over, because the air conditioning also takes power..

What is the companies job?

sometimes, LCD monitor cannt replace CRT monitor on functions.

if can replace and dont effect on work, sometines even can reduce number of the monitors and computers to save expence and energy.

is the 70F an average or constant in a year?

What lamp do they use? do they use ERPii for their managment? all need to considerade.

too vague to give answer.

this thread may be making a kidding

I have to agree with most of the other posts, there is insufficient data. In the north east the temperatures can very greatly over the area and from year to year. Last year Pennsylvania only had a couple of 0 to 10 degree F temperatures and most of the winter the temps were above 20 degrees F. If you go farther north you will get colder temps.

As mentioned a lot of the modern buildings are always in a cooling cycle as the bulk of the heat load is the lighting in the building. Also you have copy machines which have on average a 1000 watt heater in them. Another thing to consider is that most airconditioning designers take into account the quantity of human beings in the building, as most of the airconditioning load is used to reduce the humidity expelled by humans. Another issue here can be that many of the more modern AC systems control the humidity and to reduce it the AC systems sometimes have to add heat, even in summer to acheive that.

All things considered, this is a question which is unanswerable. I think the main intent is to encourage dialog, not to get a pat answer.

Cowards! (Although there is clearly insufficient data to do a thorough job, we can still give some indication.)

The office is maintained at constant temperature, so we know there is air conditioning. Heating energy costs for air conditioning used as a heat pump are comparable to other sources, so we can use that as an indicator.

In order to allow calculations, I propose the following additional assumptions:
a) that the air-conditioning is the only source of heating/cooling, and is used as a heat-pump in winter, and that the average pumped energy (summer and winter) is 300% of the input power
b) that the monitors cost them $150, and they pay 12.5 cent/kWHr.
c) that the difference in consumption is 100W for an average eight hours each working day.
d) that the office needs to be cooled for half the year and heated for the other half (this will change according to the heat-load, but is better than nothing for a first estimate)

So the CRT would have directly consumed about 10 cents worth of additional energy each working day.

During the summer, the air-conditioning would consume an additional 5 cents
During the winter, 2.5-cents would be saved from the heat-pump drive.
N.B. that this indicates that moderate variation in temperatures would not change the result by a great deal.

So, over the year, the average additional energy cost due to the CRTs is 12.5 cents per working day; assuming 220 working days per year, we have an annual saving of $27.50.

That makes the payback time (from energy alone) about 5.5 years, based on historical energy costs**. It doesn't seem to be very sensitive to small changes in annual temperatures.

**Given the life of LCD displays, that is probably too long to be viable unless it allows the company to expand without upgrading the air-conditioning; on the other hand, prospective rises in energy pricing might halve this time over the coming five years; and of course there will be additional savings in the maintenance cost and down-time of the air-conditioning system.

First! I was in the business of retrofitting lighting for 14 years with new energy efficient technology as well as motors CRT shut-off hardware and what have you.

The determination has to be made on the value of the new 17" monitors vs. the 19' monitors against the anticipated savings. 100 watts @10hrs/day times 260 work days. is 260kWh (kilo watt hours.) At 20 cents/kWh the savings would about $52/year. The 100 watt differential seems high!

There would be a reduction in air conditioning and an increase in heating which at todays cost of fossil fuel might be a wash. If the "new" monitor cost is about $200.00 your pay back period is about 4 years. By that time LED and/or organic led monitors will be available and, in my opinion, would be the time to replace them for a greater savings as well as end-of-useful-life of the 19" monitors.

In my opinion it doesn't make good financial sense.

Look for other ways to save energy! Check your present lighting system to determine if new lighting technology will give you a greater savings and pay back period. Make sure the HVAC systems are well maintained and replace failed equipment with the latest energy saving equipment.

Good luck

Despite our different assumptions about the exact location (electricity cost) and the efficacy of the purchasing department, I think we are in agreement. However, we both failed to include the effects of tax writes-off when they dump them on their favoured charities.

The answer would be even clearer if we were on the Canadian side of the border - unless there are grants from the electricity company (not too surprisingly, they prefer States-side sales).

Tax incentives and/or utility company rebates may not apply to changing monitors due to the fact it's to easy to revert back to the original 19" monitors since it's not using a "more" efficient 19" monitor. Usually, such as lighting, going to more energy efficient technology while maintaining existing lighting performance is the goal.

So, if you need 70 foot candles of lighting and reduce the number of lighting fixture to go to 50 foot candles usually will not get you a tax incentive or utility company rebate.

*Isn't that a new Italian Car?

No, that the FIAT Accomplini

<Reply to GM - hitting the "Reply" button didn't nest it...>

Noooooooooooo!

That's not the point of WEEE at all - anything Electrical you throw out now, however old, has to go through the WEEE reclamation route. This is paid for by the producers so disposal should be free at the point of recycling, although you might pay transport collection cost. If you neotiate the contract correctly, there is the possibility of a rebate from the recycling firm if "metal" prices rise.

As to the lead (Pb) content - with the price of lead at the moment, you'd think the companies would clamouring to extract it. there's enough of it disappearing from church roofs.

For heaven's, well your own, sake DON'T put WEEE in landfill - you can be prosecuted. All companies should have segregated reas for WEEE.

Ken: Most definately!!!!

Hi, English Rose!

I don't see the point of having separate areas for WEEE. When I was at university, the washrooms were all booths and co-ed. Nobody seemed to mind.

The other day, I stopped into a coffee shop to WEEE, and since there was no toilet paper in the mens', I went into the women's. Both were single-use rooms with a lock on the door. The proprietor (a woman who must've been having a hard day to begin with) went ballistic on me both on the way in & (since I paid her no mind...after all, I wanted some TP wherever I went!) when I came out. Chaq'un a son gout, I say! Separate areas for WEEE should be a thing of the past.

What we REALLY need is toilet seats that remain in the UP position and have to be lowered for seating use each time instead of vice-virtue. Perhaps then the gals wouldn't be so worried about which area the WEEE should be placed.

Mark

AAh...but when the pen-pushers see that the company is fully responsible for ANY goods purchased before the WEEE came into force, they panic. Then the laws on landfill were due to come in, which could have increased the company's liability.

Mugs answer was to get rid of as much as possible to landfill ASAP!! (On the theory that the laws were there to be avoided, rather than complied with)

Private individuals are covered by the free collection/disposal rules, companies must put in place agreements with their suppliers. (Is this so they will be tied into replacing with new goods from the same manufacturer?)

GM1964

They are saving research money by having everyone here work through all of the possibilities. That is why the manager is where he is today. Assign the task.

what is the cost of the energy per kwh? and what is the cost of the monitors?

Being in the North-East, heating costs far exceed cooling cost.

So, the lose of the heat from the CRT's will actually result in energy waste rather than energy savings.

Electroman

So how we get to every one huddled around their monitors trying to stay warm.

"So the loss of 6kW of waste heat from the old CRT monitors would need to be replaced by the heating working extra hard - and costing more?

That would be the same 6kW of heat the AC would not have to remove in the summer to cool the building. The cost of replacing this lost heat during the winter would be less not more. I don't know of to many building here in the north east of the USA that use electricity to heat the building most use natural gas. Which is cheaper. The use of a CRTs as a heat source over a furnace you tell me is more efficient?

Hi, ozzb!

"The use of a CRTs as a heat source over a furnace you tell me is more efficient"

I think the use of CRTs as a heat source would be more efficient IN the furnace. Just my opinion.

Mark

Reading this relative to your other comments: of course electric heating is the most efficient at the point of use, because there is no need for the warm exhaust gasses to be vented. On the other hand, apart fom Hydro, the generation of electricity is only 30% efficient. That means that heating via electricity is generally expensive in the USA; I believe that this is completely different from your situation in Ontario.

BTW, by the time you've reduced emissions due to burning the CRT to legal levels, you've probably lost more than you've gained

the short answer is they wont realy see any savings. why you ask well tru that LCD displays take less power to operate and generate a lot less heat than a conventanal CRT monitor but with the added cost of heating durring the fall, winter, and early spring months you will not see any significant savings untill you replace the LCD with newer ones, the elctrical savings would be immediate but the added cost of heating will eat up the savings quickly, but the reduced cooling costs would be temporary as any company knows who works in the northeast.

now as far as trhe math goes well it works like this (based on average consuption of monitors for of the specified size and type)

19" CRT Power: 125W average X 60 monitors = 7500W

17" LCD Power: 50W average X 60 monitors = 3000W

energy savings per month = 7500W - 3000W = 4500W

per year Savings

7500W X 12 = 90000W

3000W X 12 = 36000W

power savings per year = 54000W

Northeast average electrical cost is $0.170 per KWH so aproximately the savings are $918 per year or $76.50 per month

not bad.

in the summer, we have to open air conditioner to cancel the heat produced by the power, in the winter we can use this heat to compensate the funance energy.

so we still save energy of 54kw/year.

but on other side. lcd has not as fast response as crt. if you need fast response speed. you cannt replace each other.

I bought recently the lcd of response speed less than 2ms and there is less than 1ms of the lcd monitor on the market.

in spite of this, I advice you to mke clear what is response speed and what is frame rate (or field rate)

once you ever play games or watch special effect of movies. then you will know wht is fast?

and what I mean is?

C'mon! Give me a break.

(1 - 1) + (1 - 1) = 0.

The building temp is a constant 70^o F (is that about 21^o in real temperature?) year 'round. The on-off times for the monitors aren't given, so we have to assume that both types run for equal amounts of time on a year-round basis, and devil take the yearly time allotment for warm and cold seasons, also not given...not even the latitude or longitude of the business, so it's fair to imagine there's a winter and summer, as we all seem to be doing anyway. OK: winter 50%, summer 50%...I'm easy about that!

The CRTs give off heat in winter, contributing however minisculely (is that a word?) to the building's heat. In summer, that miniscule amount must be offset by the air conditioning.

Break even.

Now, scrap the CRTs and bring on the LCD's (whoops! should'a waited for plasmas!). What've we got? Units giving off an even more miniscule amount of heat to affect the heating of the building in winter in an even more miniscule way and the air conditioning of summer in an even more miniscule way.

Break even again!

How long will it take for energy savings to pay for replacing the CRT's? Never. It's an expense that solely relates to upgrading and modernization. One could better have calculated any savings by noting the additional desk space afforded by the LCDs.

Sheesh!

Mark

Break even.

Mais non!

It can be below 32 (Foney degrees) virtually all the time for more than 6 months, in the real northeast, where men are men and most women are too. Thus, the temp needs to be raised by 38 degrees. In the summer, it's rarely over 80, so the temp needs only be lowered by 10 degrees.

You can see from this link that the average annual temperature in Boston is 51.3 degrees, so there is a decidedly bigger need for heat. But Boston is "down south" where people with weak constitutions live (as is Toronto). Real men (and menwomen) live in places like Caribou Maine, where the average temperature is a more invigorating 38 degrees (about 3 Crazy degrees).

So in the real northeast, workers cling to to their CRT monitors to stay warm, winter and summer. Providing LCD monitors would lower productivity, leave psychological scars, almost certainly cause poor health, and might subject the company to OSHA fines.

Despite all this, I strongly agree with your TP comments, and I am certainly not going to spend any time in Rose's loo.

Also, I think you said "chalk causes gout". I think it is actually caused by a buildup of uric acid, (so I can see how it fits into the conversation) rather than chalk.

Hi, Blink!

Nope, I'm not the one who ventured chalk as a gout promoter. I'm totally with you on the excess uric acid line of thought. I think Rosie would be wonderful to visit, but perhaps we should 'go' before we get there. And bring roses.

While a lot of men in Toronto are --based upon observations during gay pride day and in malls where cross-dressers in this liberated city unabashedly shop-- quite probably at least desirous of being women, my experience has been that a lot of them are quite happy being men too. During summer, however, Toronto is a very warm place, and it's very possible (thank goodness for summer!) to determine that the women are women, even the ones that are men. In Maine, it's a little more difficult to tell, because often you can't see any of the people for the trees in the way, so we sort of have to take their word for it.

In the challenge, no one has given us the heat contribution of either variety of monitor, so we don't know what their contribution to the building's energy use is. It's therefor fair to postulate that there isn't any real temperature figure required in the solution.

What we do have is a screen size. Let's suppose that the CRT monitors with the larger screens give off "more" heat. In the winter, they contribute a 'heat' of as much as 19, and in summer, they cost a 'heat' of as much as 19. Similarly, the LCDs contribute a max 'heat' of 17 and cost a max 'heat' of 17. From this, we can deduce that the extreme temperature differential contribution caused by replacing the monitors is 17/19 for cooling and 19/17 for heating (or vice virtue, it really makes no never-mind which gives off more or less heat). So...'break even' during the continuum of a year, even through the interim ambient temperature fluctuations.

No savings due to heat differential.

Mark

Break-even in only terms of total heat energy supplied to room (total is always zero if the temperature remains constant?). Not break even in terms of total energy supplied from utilities or combustibles, nor in terms of total cost. The difference in total heat supplied is simply in the heat that is wasted. The difference in cost comes from the company's bank account. Neither savings nor environmental benefits ever exceed the unnecessary cost/pollution in producing/disposing_of extra screens.

Give us a break, more like - have you ever walked past the coolers for an air-conditioning system? Where do you think all that heat is coming from? That's right, some of it is being pumped out of the room, and some of it is from the mains - the power required to drive the pump.

So, if you add an un-needed source of heat into the room, not only does the air-conditioning fail to deliver power back into the mains, it takes additional power. Your "negatives" are not given back to the mains to make any savings on the electricity bill, but pushed into the environment - where they are not wanted. On top of that you pay extra for the energy required to drive the heat-pump.

On top of that, during the winter heating via electricity is also more expensive than most other methods - except in the vicinity of a hydro-electric power source. The challenge specified North-East USA, so you can look up the prices there for yourself.

Hi, Physicist? !

I think you might be trying to disagree with me, but I'm not able to determine where...since what I think you're saying in your reply is what I think I said that you're replying to. (Both sets of monitors affect the internal building temp and energy supply and must be adjusted-for in a consumption estimate. No?)

However, all those things being said and the choices made about where and when the energy exchanges take place, the challenge really doesn't offer any hard data; so if you choose to chase a "correct" response by data mining elsewhere, you might be misled in doing so, for the "correct" answer must then involve a wide range of data depending upon which answer found what and where, and what was plugged in to whichever formulae were used and how they were used to determine the response. All very individualistic and uncertain in terms of finding a definitive answer. And all potentially correct to some degree or another. Or not.

I think data mining and inductive reasoning for finding a realistic response to the challenge is just fine, if you want to go that route. And I really like the answers that have been determined in that fashion. By sticking only with the data given, I'm looking for a more superficial method of responding to the challenge by restricting myself only to the information given. For example, "North East" in the challenge is nice, since I too like the North East area of the USA. But since it offers no more data than a location, and not even a comparison with another location, it is not useful or complete data...and I consider it to be a red herring. <---[That's me eating the herring!]

As far as 'right' and 'wrong' answers is concerned...I've been on both sides of that fence lots of times in these challenges, and the best thing about them is that regardless of which side I land on, the trip has been great fun.

Mark

Hi Mark

Maybe we are talking at cross-purposes. I read your response as saying implying that we could not know if there was any saving at all.

What I am trying to say is that the only condition under which there could be no savings is if both the following statements apply:
. That the screens are turned off whenever air conditioning has to provide cooling** to maintain the room at the constant 70^O.
. The heat that the CRTs generated (over and above the heat generated by the LCD screens) is replaced by energy from an equally costly source.

As there is no part of the NorthEastern US that never goes above 70^O, the first of these demands some pretty odd behaviour.
Similarly, as there is no part of the NorthEastern US where daytime electricity is regarded as an economic heat source, even the replacement of CRT heat by non-heat-pump electrical heating or any other equally costly heat source is unlikely.

So, I have no problem with your saying that it is possible to avoid making any savings; but to give this as the expected situation without stating the assumptions seems perverse.

On the other hand, I cannot see that this change-over would make either financial or environmental sense - unless the CRTs were becoming costly to run for other reasons, or the air-conditioning was unable to cope with an increased heat load that was needed for the company's expansion.

Fyz (being the closest emoticon to a practical electricity-free cooling method in the summer)

**Basic thermodynamics show that you cannot convert heat to electricity at 100% efficiency under any conditions whatever. In reality the situation is worse than this when cooling a building, as the air that you wish to cool is often cooler than the environment where you wish to dump the heat; under these conditions, basic physical laws show that additional energy is required to effect the transfer.

Hi, Physicist? !

"under these conditions, basic physical laws show that additional energy is required to effect the transfer"

The energy expended to operate a system of heating/cooling for the CRT monitors has been in play, presumably, for some time, and averages out with a resultant 21^o (70^o F_unny) constant.

When the changeover is made, the same exact system will operate the same exact way, but compensate for a little more --or, less-- heating and cooling relative to the load placed upon it by the new LCDs.

So the amount of additional energy being required for one variety or another of monitor for either heating or cooling can be more, and it can also be less. The laws of thermodynamics remain unchallenged , and the application of energy still varies .

"That the screens are turned off whenever air conditioning has to provide cooling** to maintain the room at the constant 70^o"

In normal operation, sometimes the air conditioner will turn off and on (not the monitors ...that would be impractical), and sometimes the heating too, will turn off and on to maintain the constant temperature regardless of what the monitors alone are doing. (There are also people milling about, some carrying coffees or cold drinks, changes in temp outside the building, lighting and copy machines, power breakdowns, etc. etc.; and we don't get to consider 'turning on and off' those variables, so the thermostat has to make the decisions .) Thermostat! Throw in another complication !

Good thing we're given an average, 'cause that's all we have to go on!

The particulars are intriguing and make for a whole host of assumptions and lovely mathematical explanations.

To overcome the complications one needs must develop an overview that doesn't get too bogged down in the necessary details, yet retains a modicum of sense to it. Occam's razor, kiss, call it what you will.

I think a good clue-word in developing a kiss overview is "comparisons". Two varieties of an item each having a singular size and temperature range (warm up, usage, cool down all averaged in), and all 60 of each variety exhibiting constant working temperature over the course of the year, just as the building's ambient internal temperature was given as a single unit. Fair is fair (<---assumption).

How else would you create a comparison that explains the difference over a year's time with (apparently) random 'up/down...on/off' application of t_(ebuilding) energy application changes depending upon an unspecified seasonal adjustment plus typical --but unspecified-- additional 60-machine usage with each machine using its own individual 'up/down...on/off' heat dynamics humming away inside?

Might you substitute 17X and 19X for the difference in the monitors' activity as it affects the need for rising building temperature dynamics in your equations [and maybe 17y and 19y for the cooling affects]?

Would you in that case...since you don't know which is the 'hotter' monitor unit (or you could assume you did, since the question hints at a potential savings due to changeover) be tempted to use '+/-' signs in each equation, like t_(ebuilding) +/- 60[17X (+/-17y)] = 21^o? Or just stick with something simple, like 60(17X )+ t_(ebuilding) = 21^o ?

And/or since the 21^o is a given constant and the only thing affecting it in the challenge is the monitors, perhaps also ignore what's going on outside the building, temperature-wise? (<---mmmm....kippers!)

When all's said and done, asks the challenge, would it eventually pay to make the changeover ?

Just askin' .

Mark

Hi Mark

So far as I can see, just one of your points has any possibility of resulting in zero savings (or higher energy costs). This is my point 1) below. Everything after that is pretty-much the result of the situation - though doubtless a perverse operator could find a way to waste additional energy - and attribute it to the changeover; but I can't find any conditions under which that attribution would be valid.

1) Even on the basis that "everyone knows" that 17" LCD screens consume less power than 19" CRTs, Occam/KISS would demand evidence that this could be wrong. Nevertheless, I have wasted a little time checking this out, and the highest power 17" LCD I came across was rated at 40/2 Watts. This is less than any 19" CRT I know of. If you can find a pair of screens that serve as counter-examples, I would accept your uncertainty, and the remainder of this post becomes irrelevant.

2) To simplify calculations, I would only consider the difference in power. Based on 1) the change-over to LCD screens means the power provided to the screens will be reduced. For the purpose of this particular argument (not the challenge) the size of this reduction is not important - as all I am trying to show is that there will be some savings in energy costs.

3) Based on the building temperature being held to 70^O all the year round we know that the building must have air conditioning.

4) During cooler periods, the difference in dissipation between the screens represents heat that must be replaced. The air-conditioning units can be used as heat pumps to replace this heat, using (at most) 2/5 of the input power. It could be that other heating methods are used, but (unless you assume unbelievable stupidity) the energy source that these use will never be more expensive than the electricity that drove the screens.

5) At some times of the year, cooling will be required even with the LCD screens. During these periods, the entire difference between the power required for the screens will definitely be saved. When the higher-power screens were used, the additional heat would all have to be pumped to the outside, which would have used further additional power

So, unless you can refute my point 1), there will definitely be power and cost savings during the warmest periods of the year, and at worst the costs of providing power will not rise during the remainder of the year. That equates to a saving - and I can't find any simpler conditions that correspond to the requirements of the challenge. KISS or Occam, whichever grabs you.
[That is not to say that the change-over was financially or ecologically viable]

Can I just ask, Why replace 19" viewable area screens with the smaller 17" screens?

If my employer did that to me, I'd tell him to pull his head out of his arse, and get real screen sizes.

Its bad enough using the 21" CRT at home, then going to work and using the 19" LCD's

19" CRT screens are usually closer to 17½" viewable area, so a 17" LCD is equivalent.

I'll do another approximation and try to use the AC efficiencies as i can.

I've got a search of statistical data about northeast usa and here are what i have found:

Average yearly lows : 24^oF (terrestrial) .. 47^oF (coastal)

Average yearly highs: 49^oF (terrestrial) .. 66^oF (coastal)

As we know nothing about location of company i must reaverage these as:

mean temperature of winter = 36^oF and that of summer = 57^oF.

I will use winter/summer ratio as 6 months / 6 months (It is possible using montly statistics though..) and duty time of 8 hours per day, total 1440 hrs /6 mnts

I will accept the power ratings as 125W of CRT and 40W of LCD as i did in (#9), but i will assume the heat counterpart of CRT's power as 30%, near lower limit for this time.

Say each monitor is placed in a 5m² area and height of floor is 2 mt, means each monitor is in a 10m³ volume. I will use this value for the simplicity of math, this is not a key point though.

Energy required to heat the air of 10m³ by 1 ^oF will be

ΔQ= ρ*V*c*Δt = 1,2(kg/m³)*10m³*1(kJ/kg)*1 = 12kJ/^oC = 6,67 kJ/^oF (i've used the ρ of 1,2 kg/m³ and c_p of 1 kJ/kg.^oC, both for air @20^oC).

Efficiency of heat pump;

in winter: 1+(36/(70-36)) = 2,1. Then power consumed by heater ≈ 3,18kJ /^oF.

in summer: 1+(57/(70-57)) = 5,38! although i've heard about efficient ACs up to 6 but this is not general. I'll accept a max efficiency of 3,5. Then the power used by heater ≈ 1,90kJ /^oF.

Now start with CRTs exist:

Monitors consume themselves are 0,125kW*60 = 7,5kW-h per hour.

Heat counterpart of power = 125*30% ≈ 37W = 0,037kW. This will heat up the air of 10m³ along 1 hour by:

0,037*3600 = 133,2 kJ => Δt = (133,2kJ / 12kg)*9/5 = 20^oF.

In winter, the initial temperature near monitor will be 36+20 = 56^oF (instead of 36^oF). This means we can use the maximum efficiency of 3,5, as we will do in summer and;

Energy consumed by heater: 1,90kJ*14^oF*60 = 1596kJ = 0,44 kW-h per hr.

In summer the temperature above mentioned will be 57+20 = 77^oF, that is, even the ACs are reversed to cooling. We can accept the efficiency as 3,5-1 = 2,5 with this conditions (=Max cooling efficiency).

Energy consumed for cooling of 7^oF : 12*7*5/9*60*(1/2,5) = 1120kJ = 0,31kW-h per hr.

Energy used while crts exist will be;

in winter: (7,5 + 0,44)*1440 = 11434 kW-h

in summer: (7,5 + 0,31)*1440 = 11246 kW-h

yearly totl.......................... = 22680 kW-h ...w/CRT

While LCDs exist:

Energy for LCDs = 0,04*60 = 2,4 kW-h. Heat pump will be operate at 2,1 efficiency in winter and at 3,5 in summer. Energy consumed by heater will be:

3,18(kJ/^oF)*34^oF*60 = 6480 kJ = 1,8 kW-h and 1,9(kJ/^oF)*13^oF*60 = 1482kJ = 0,41 kW-h respectively. Then;

in winter: (2,4 + 1,80)*1440 = 6046 kW-h

in summer: (2,4 + 0,41)*1440 = 4046 kW-h

yearly............................... = 10092 kW-h ...w/LCD

The yearly energy saving will be 12588 kW-h with a duty of 8 hours per day. I don't know the cost of electricity but Guest(#33) have been used a value of 0,17 $/kW-h. With this cost yearly saving will be 2140 $. This is approximately cost of 10 LCD.

10 LCD per year yields a result of 6 years!

If we don't concern with climate then the gain would be 12 LCD per year and would yield result of 5 year simply..

If we used the heat portion of CRT as 60%, result would differ by 40$ per year only...

The main part of result is always regarding the power ratings of CRTs and LCDs, remaining has no worth!

I think this is a play of "who knows what!"

I vote you, because too much calculation. although I cannt read most of them.

Hi, feridun!

Well, you've assumed the power consumption for building temperature maintenance, assumed a statistical temperature variance for a fairly good-sized area (that leaves a warm winter and a cool summer so probably you should check these figures though), possibly assumed which general CRTs and LCDs you chose to be used to calculate your results or possibly averaged a few, assumed the variation in temperature over an assumed seasonal change, and created heating and cooling for a building of 6,000 m³ with a single monitor in every 10m³ of the building, adding some measure of reality by surmising the building's heating costs; and noted that the interior temperature remains unchanged year round during both the reign of the CRTs and LCDs.

And, you have accurately arrived at a distinct savings in doing so. The method you used is admirable.

As far as being a "play of "who knows what"" is concerned, when you think about it, the challenge doesn't seem to offer enough information to know anything, really, about the situation without assuming a lot, does it?

I like your solution process, though. If you're really keen, try reworking it with an average for winter of 32^o and summer of 70^o (0^o and 21^o)...probably more realistic, just as an additional challenge. Your working this solution by using inductive reasoning to arrive at your figures from the given information is really well thought out.

Since these challenges, flawed as they are, usually require us to arrive at a definitive answer, it's unlikely to calculate an in-depth response that will agree with any of us.

Mark

Hi Feridun

I don't understand some of what you have done here.

First, I don't understand what you mean by "the heat counterpart of the CRT's power". All electrical power supplied to the CRT ends up as heat, and nearly all of it inside the room. Or are you referring to the CRT spending 70% of its on-time in an energy-saving mode? (I feel I'm missing something serious here - because I could not find an interpretation that gave savings of $2140 per year at 30% and only $40 more [=$2180 per year] at 60%)

Then, I don't understand where the volume of the air comes in. To my mind, once you maintain constant temperature it doesn't matter how much air is involved. All we are concerned about is power balance. If I were to convert to temperature and back again, the only effect would be that I made more arithmetic errors.

Even if you are allow the building to cool or heat overnight (sensible but in contradiction with the challenge as posed), it should not affect the answer, as the equipment should not be turned on until the air temperature has stabilised. Incidentally, the thermal capacity of the air is unlikely to be anywhere near as great as those of the building and the equipments (even wooden floor-boards would have a heat capacity exceeding 10-kJ/sq.m/^OC), but even so, once the air has achieved its required temperature, changes to the sources of heat will not affect the total power that needs to be delivered to the room.

Fyz

Hi Physicist?,

Firstly i must indicate that this is reply for your 1954th post and 1954 is the year i was born! Mysterious?

Now lets go with your comment...

• "First, I don't understand what you mean by "the heat counterpart of the CRT's power". All electrical power supplied to the CRT ends up as heat, "

Do you mean that all of the power consumed by CRT spreaded out as heat?

No matter, then u can use the ratio of 100% instead of 30%. I have tried to find an approximation to solve the challenge merely, and used the 30% as an example.

• "and nearly all of it inside the room."

How much volume of room? Do we know about the room?

• "Then, I don't understand where the volume of the air comes in."

This was also a sample volume. You can use any value of volume that the CRTs heats up.

• "To my mind, once you maintain constant temperature it doesn't matter how much air is involved."

Do you assumed that that the ACs - or whatever the heater/cooler is- are working along 24 hr? Do we know this?

The only statement of the poster is "They keep the building temperature at 70^o F year round."

Is this same as "they will keep the ACs operating all day long"?

• "All we are concerned about is power balance."

Yes you are right! And this is what i've done.

• "If I were to convert to temperature and back again, the only effect would be that I made more arithmetic errors."

I have applied one way conversion only, no back-ing again.

• "Even if you are allow the building to cool or heat overnight , "

I have not assumed that the workplace is cooled or heated overnight. Simply try to find the power balance.

• "(sensible but in contradiction with the challenge as posed), it should not affect the answer, as the equipment should not be turned on until the air temperature has stabilised."

Why in contradiction? Is this workplace is located mexico actually but i have imagined it in northeast usa?

Do you know a company that waits if the temperature raise/fall to a point fixed initially for and then start to work?

• "Incidentally, the thermal capacity of the air is unlikely to be anywhere near as great as those of the building and the equipments (even wooden floor-boards would have a heat capacity exceeding 10-kJ/sq.m/^OC),"

Is this challenge about finding the transient responses for climatic events?

• "but even so, once the air has achieved its required temperature, changes to the sources of heat will not affect the total power that needs to be delivered to the room.but even so, once the air has achieved its required temperature, changes to the sources of heat will not affect the total power that needs to be delivered to the room."

What is the total power composed of? Don't you count of power consumed by CRTs whilst you agree that all of their power are spreaded as heat.?

Thank you for your reply my dear, i hope i can answer for your doubts.

Best regards

f.h.

Hi Ferridun

>Firstly i must indicate that this is reply for your 1954th post and
>1954 is the year i was born! Mysterious?
No mystery I can find. Given even a small set of numbers that are significant to you, you might expect this sort of thing to happen up to several times a year (although this would depend on how many numbered communications you see). How often you would notice is another matter...

>Now lets go with your comment...
>>First, I don't understand what you mean by "the heat counterpart of
>>the CRT's power". All electrical power supplied to the CRT ends up as heat
>Do you mean that all of the power consumed by CRT spreaded out as heat?
I mean that all of it converts to heat within a few seconds. Energy leaves the CRT mostly already converted to heat; the small amounts that are in the form of air movement or radiation are soon converted to heat; the only part of the energy that does not appear as heat in the room is the small amount of light that escapes through the window - and this will not be very different for the LCD
>No matter, then u can use the ratio of 100% instead of 30%. I have
>tried to find an approximation to solve the challenge merely, and used
>the 30% as an example.
That would be fine if I could understand why there is such a small difference between 30% and 60%

>>"and nearly all of it inside the room."
>How much volume of room? Do we know about the room?
>>Then, I don't understand where the volume of the air comes in
>This was also a sample volume. You can use any value of volume
>that the CRTs heats up.
I can't handle this: first you ask what is the volume of the room, then you say I can use any volume I choose. Is the actual volume of the room relevant or not?

>>To my mind, once you maintain constant temperature it
>>doesn't matter how much air is involved.
>Do you assumed that that the ACs - or whatever the
>heater/cooler is- are working along 24 hr? Do we know this?
>The only statement of the poster is "They keep the building
>temperature at 70^o F year round."
>Is this same as "they will keep the ACs operating all day long"?
The norm would be to turn the heating/AC on soon enough that the building is comfortable when people arrive for work. Historically, the facilities manager would have adjusted a timer according to the season. However, almost any facility equipped in the last 15 years would have a controller that turned the system on according to the building temperature. What you may be certain is that the room is almost always warmer than 62^O when the staff arrive (or they wouldsurely go back home). So the equipments will be turned off most of the time the building is heating

>>All we are concerned about is power balance.
>Yes you are right! And this is what i've done.
>>If I were to convert to temperature and back again, the only effect would be that I made more arithmetic errors."
>I have applied one way conversion only, no back-ing again.
By power balance, I meant maintaining zero net heat into the room from all causes, including of course the heat from the external environment.
You seem to be working in units of air temperature, so everything has to be converted to air temperature. But your answers have to use kWh to get to a financial amount; so you are converting back to kWh, however you hide this.

>>Even if you are allow the building to cool or heat overnight
>I have not assumed that the workplace is cooled or heated
overnight. Simply try to find the power balance.
It looks as if f you are calculating how much you have to heat the air to recover from the heating/AC having been turned off overnight. Is this incorrect?

>>(sensible but in contradiction with the challenge as posed), it
>>should not affect the answer, as the equipment should not be turned
>>on until the air temperature has stabilised.
>Why in contradiction? Is this workplace is located mexico actually but
>i have imagined it in northeast usa?
Having the screens turned on while the building is changing temperature is in contradiction to any interpretation I can find of "They keep the building temperature at 70^o F year round"

>Do you know a company that waits if the temperature
>raise/fall to a point fixed initially for and then start to work?
It's called planning: you ensure that the heating/AC is turned on soon
enough so the staff don't turn around and leave as soon as they arrive.

>>Incidentally, the thermal capacity of the air is unlikely to be anywhere
>>near as great as those of the building and the equipments (even wooden
>>floor-boards would have a heat capacity exceeding 10-kJ/sq.m/^OC),
>Is this challenge about finding the transient responses for climatic
>events?
I'm not sure whether you are being inconsistent or simply unclear. In any event, this comment bears no relation to my concerns.

>>but even so, once the air has achieved its required temperature,
>>changes to the sources of heat will not affect the total power that
>> needs to be delivered to the room.
>What is the total power composed of? Don't you count of power
>consumed by CRTs whilst you agree that all of their power are
>spreaded as heat.?
Yes, that is precisely what I did in post #21. I calculated (approximately) the cost of the power that was required to replace the difference between CRT power and LCD power when the system was heating, and the cost of the power to remove this heat when the system was cooling. I assumed that the rate of air-replacement etc, was unchanged.

>Thank you for your reply my dear, i hope i can answer for your doubts.
Unfortunately, not so far.
BTW, "my dear" tends to be taken as condescending in this part of the world, and so is probably best avoided.

Best regards

Fyz

Hello Physicist,

I passed 1st paragraph (off topic).

2nd paragraph:

"That would be fine if I could understand why there is such a small difference between 30% and 60%"

This part is pasted from (#49):

while CRTs exist:

in winter: (7,5 + 0,44)*1440 = 11434 kW-h

in summer: (7,5 + 0,31)*1440 = 11246 kW-h

yearly totl.......................... = 22680 kW-h ...w/CRT

if we accept 60% then CRT portion of heating raise to 40^oF. This means ACs are in cooling mode even in winter and the value of 0,44kW-h will be changed to 0,31kW-h. and the result of 12588 kW differ by 188kW-h and 32$ per year. And yes! You are right at this point that i have had not get into account the power of coolers in summer while i was throwing the value of 40$ as a guess.

The true solution for summertime:

Energy consumed for cooling of 27^oF : 12*27*5/9*60*(1/1,5) = 7200kJ = 2kW-h per hr instead of 0,31kW-h (I have accepted value of cooling efficiency as 1,5).

The yearly difference of energy is getting bigger to the value of 14834kW-h and the difference between usages of 60% and 30% of CRT power raise to 382$ per year (Result is closing to that of simple solution of 5 years).

3rd paragraph:

"I can't handle this: first you ask what is the volume of the room, then you say I can use any volume I choose. Is the actual volume of the room relevant or not? "

Actual volume of the room is relevant of course. But which value of volume i must use? There is noting about either room or volume in the post. I have no way except using an imaginary sample volume that you can use yours...

4th paragraph:

(Nothing pasted here.)

In fact i have not concerned if the climators are active overnight or not. This will change the value of initial temperatures i have accepted only. All i want to do is how does change the power consumed by heaters/coolers while CRTs or LCDs exist in the workplace, and i have also not get into account above mentioned power for "out of duty" part of the day why this would have been not important with the CRT/LCD usage point of view.

5th paragraph:

"By power balance, I meant maintaining zero net heat into the room from all causes, including of course the heat from the external environment."

Power balance is what you meant above actually. If it were about finding the total energy necessary for heating/cooling of a well specified workplace/volume initially with challenge then be sure i would be tried to find the power balance but it is "energy saving" of LCDs against CRTs with a given temperature of 70^oF and nothing else. Do how you can!

"You seem to be working in units of air temperature, so everything has to be converted to air temperature. But your answers have to use kWh to get to a financial amount; so you are converting back to kWh, however you hide this."

mmm, might this be the difference between a physicist and an engineer? or do you prepare "tricky questions" for engineers?

I have converted the electrical energy to heat form. Surely there may be errors, at least rounding error.

Then i've used this form to find the efficiency of ACs coarsly and used this efficiency to find the consumed energy by ACs. This point might be tricky that you can talk about re-conversion to electrical form of energy and conversion errors. Yes, this is a conversion at the end why i've used the temperatures found via 1st conversion. Now which is bigger, the arithmetic errors from conversions or errors from formulae of efficiency itself ? My vote for second...

6th paragraph:

"It looks as if f you are calculating how much you have to heat the air to recover from the heating/AC having been turned off overnight. Is this incorrect?"

The 4th answer also suits here rather than a new one by me.

7th paragraph:

Seems that these parts of our comments because of interpreting somethings differently. This is normal and i will pass.

"It's called planning: you ensure that the heating/AC is turned on soon
enough so the staff don't turn around and leave as soon as they arrive."

Okay, i agree with planning.

8th paragraph:

"I'm not sure whether you are being inconsistent or simply unclear. In any event, this comment bears no relation to my concerns."

Do you want me to get into account, an instant change on the heat capacity of something being in the volume i've used in solution, which has a result of 5 years?

If the duration of event and new factors are available then i could try the new factor of capacity for the this portion of period of course, but;
Again we are falling the same hole of challenge. Which statement in the post does yield me to count a transient behaviour?

9th paragraph:

"Yes, that is precisely what I did in post #21. I calculated (approximately) the cost of the power that was required to replace the difference between CRT power and LCD power when the system was heating, and the cost of the power to remove this heat when the system was cooling. I assumed that the rate of air-replacement etc, was unchanged."

I'm aware of your post and also many of others. The basic part of solution is clear for everyone here. On the other hand there are many comments regarding heating / cooling methods. After reading these posts i've decided to try an approximation using performances of ACs and arrived at a point that all math regarding ACs does affect only a part of 20% of the result! Means the result may be anywhere in 4..5..6 years.

You(and me) have can reach the big part of 20%. If anyone use a method which can reach the lower part of 20% that will be the real carnival!

And the last paragraph:

"BTW, "my dear" tends to be taken as condescending in this part of the world, and so is probably best avoided."

This is not what i want to make feel of course. Excuse me! and thank you to have made it clear for me. Possibly i have phrases used mistakenly with my other comments and i hope some guys warn me.

I enjoyed really, thank you again.

Best regards

f.h.

"2nd paragraph"
Unfortunately, your reasoning that creates the numbers remains (to me) impenetrable, and I did not find the clue in the numbers that would allow me to unravel what you have done.
I suspect, however, that what has happened is that somewhere a sign has been transposed.

So I'll ignore what the heat is used for, and just show the differences:
. the units aren't given, because they can be Watts, Joules, kWh, or whatever - so long as they are all the same

Wanted heat = H
. if heat needs to be extracted overall, H will be negative
Heat from CRTs = C
Heat from LCDs = L
Heat needed from heat pump (CRT) = H-C
Heat needed from heat pump (LCD) = H-L
Positive values represent the air conditioning pump used to heat, negative values represent the air conditioning used to cool.
If we take the heat-pump efficiency as E, we have:
. according to this definition of efficiency, an efficiency of 1 would mean that the system could not provide cooling. Some people prefer the alternate defninition

If heating, additional power/energy supplied to air conditioning = (H-C)/(E+1) or (H-L)/(E+1)
If cooling, additional power/energy supplied to air conditioning = (C-H)/E or (C-L)/E
. . . note change of order, which represents that that the energy/power supplied to the air conditioning is always positive

So the reduction in total consumption will be as follows:

Case1 - additional heating always needed:
. C - L + (H-C)/(E+1) - (H-L)/(E+1) = E.(C-L)/(E+1)
Case2 - additional heat needed when LCD is used, but cooling needed when CRT is used
. C - L + (C-H)/E - (H-L)/(E+1) = C.(1+1/E) - E.L/(1+E) - H.(1/E - 1/(1+E))
Case3 - cooling always needed
. C - L + (C-H)/E - (C-L)/E = (C-L).(1+1/E)

We may note that the saving is greatest for case 3, and smallest for case 1. This means that the proportion saved will increase as the heat from the CRT increases, not reduce as your figures seem to show.

3rd Paragraph:
You must use zero temperature change for the air in the room, as this is in the United States and the room temperature should be correct before the screens are switched on. That means that the volume of the air in the room is completely irrelevant. All we are interested in is the continuous heat loss through walls, floor, ceiling, windows, and air exchange. In the end, the only difference this will make is that heat will need to be removed for a larger par of the year than would be the case during any period that might be correcting the temperature of the air.

"You seem to be working in units of air temperature, so everything has to be converted to air temperature. But your answers have to use kWh to get to a financial amount; so you are converting back to kWh, however you hide this."
mmm, might this be the difference between a physicist and an engineer? or do you prepare "tricky questions" for engineers?
None of the engineers I work with would make any conversion between units if it could possibly be avoided, so I can't see that it is a difference between disciplines. Their reason is the same as mine: that it creates additional opportunities for (gross) human error, and it makes the work harder to explain. The norm is to convert everything to units of energy (be it Joules or kWh), as that represents only a single conversion to any of the other things that might be relevant (heat into volume of air, power, or money).
Note that systematic/arithmetic conversion errors will not be an issue, as they would cancel out - we are only talking here about opportunities to make "careless" mistakes (such as using completely the wrong conversion somewhere, of which even even[?] NASA have been guilty on occasion).

Sorry i've replied lately.

". . . note change of order, which represents that that the energy/power supplied to the air conditioning is always positive "

Of course yes, we want to find the difference of these "positive energies" for CRTs or LCDs exist.

I will try to answer using your equations:

The second side of

".C - L + (H-C)/(E+1) - (H-L)/(E+1) = E.(C-L)/(E+1)" is wrong, this must be:

C - L + (H-C)/(E+1) - (H-L)/(E+1) = H/(E+1)

(why with no CRT or LCD this must yields H=H)

Take account of case1. This equation must be solved with different values of efficiencies.

I will use additional symbols like H_c and E_c those are heat from heat-pump and efficiency while CRTs exist. Then your equation leads:

C + (H_c-C) / (E_c+1) = H / (E+1) →

C*E_c + H_c = H*[(E_c+1) / (E+1)] → H_c = H*[(E_c+1) / (E+1)] - C*E_c

This means while another heat source does exist, the energy would be used for heat-pump would be as less as C*E_c (and inversly proportional with ratio of efficiencies).

I've tried to find values of these efficiencies coarsly with reply #49 using necessary energy to heat up a sample volume by 1^oF and have used this value to arrive a numerical value of energy.

"This means that the proportion saved will increase as the heat from the CRT increases, not reduce as your figures seem to show."

This is also not true why an unnecessary energy will be used for cooling during summer especially and even during winter, of course if you don't mean the regaining time because it is inversly proportional.

" You must use zero temperature change for the air in the room, as this is in the United States and the room temperature should be correct before the screens are switched on. That means that....... "

I did not concern the habits of persons while trying to find a solution for this challenge. You might be right or not, i don't know and this might affect the interpreting of question but again, i've not concerned.

" ...... Note that systematic/arithmetic conversion errors will not be an issue, as they would cancel out - we are only talking here about opportunities to make "careless" mistakes (such as using completely the wrong conversion somewhere, of which even even[?] NASA have been guilty on occasion). "

I think u have been lazy to track the math in #49 .

You are getting nearly as bad as I am. What you have done is use H (defined as the total amount of heat required in the absence of the CRT or the LCD) and ΔH_in (the change in input heat required from the air conditioning) interchangeably.

Perhaps I should have written before each of my lines:
Reduction in electricity consumption =
but I rather thought that the sentence preceding the lines made this unnecessary.

Although it is not common practice, it would perhaps have been clearer if I had used the identity sign (≡) to show that the individual lies were purely algebraic reductions.

So my expression would be written:

Case 1
Reduction in consumption electricity =
C - L + (H-C)/(E+1) - (H-L)/(E+1) ≡ E.(C-L)/(E+1)

In this case that would be the same as C-L + ΔH_in/(E+1), but I don't see that as adding any information.
I see that you want to take into account the variability in efficiency of the air conditioning. This is reasonable in principle, but (in my view at least) an unnecessary refinement; this is partly for the reasons given below, but mostly because reasonable ranges for efficiencies and temperatures save between 50% and 80% of the change in input power, so we can use the 65% average without materially affecting the result (that is by comparison with the unknown price point of the screens (e.g. robust anti-reflection glass versus economy, dead pixel limit ...).
Assuming that I read your text correctly, the way you are trying to do use changes in efficiencies does not correspond to the situation. The reason is that the heat pumps in the air conditioning are either on or off, and pumping between the room and the outside; as neither temperature depends on the presence or absence of the CRT/LCD, only a single value of efficiency should be used for either of cases 1 or 3. There will however be a change for case 2, because the temperatures of the heat exchangers will depend on the direction of energy flow.

I don't think you made errors in conversions of #49, but this just complicates the explanation without (so far as I could see) added benefit.
My real problem was the high level of what appeared to me as ambiguities in the reasoning behind the presentation of the expressions, so I couldn't draw any conclusions.

Hi Physicist,

It must be why i've problem with refreshing . Yes, i'd interpreted the "H" as total amount of heat as you told, pardon me.

It will be better to try to explain my way of solution.

I assumed that every monitor is working in a sample volume of air - of 10m³-.

I've calculated the required energy -h_u-to heat up this volume by 1^oF and all the math relay on this!.

I've calculated temperature difference ΔT at this volume cause of H_c -heat energy from CRT-, ΔT = H_c / h_u [kJ / ^oF] .

I've also found a value of efficiency approximately using this ΔT why i've had no idea what could be the efficiency of ACs about, i did not want to refine the solution though.

Then i've calculated the energy consumed by ACs separately according to seasons while monitors exist and not.

As you can see the key point with my approximation is the sample volume that i've used. I've also not concerned with isolation, losses of heat, etc, because these would be same for both of situations that monitors exist or not. In fact it would be more accurate if i'd used ratios of "H"s instead of differences but i've contended with the difference of those energies regarding CRTs and LCDs without more refinement.

I hope i've made it clear this time .

Best regards

If the local temperatures are low enough, it will even out because the CRT's would have been helping to heat the place. No point using energy - saving light bulbs in winter, because incandescent's will help to heat the home.

Apologies if this has been mentioned before - I didn't read many of the posts.

Hi, Physicist? !

I think you know what I posted. (But just in case, the contribution of the CRT's to summer cooling is to raise the cost of it. So yes, I really mean my 'apparent implication' that CRTs contribute to summer cooling. )

"Do you really intend to support of posts that don't consider the possibility that cheaper sources of heat than daytime electricity may be available?"

--Not sure if this part of the question is intended for me. Did I say somewhere that I don't support the possibility that there are cheaper sources of heat than electricity? Is this a question about this blog set? I hope you aren't just jumping on some phrase or another that I wrote and making something else out of it. (My own favourite --in terms of bang for the buck-- is closed-system hot water radiators with natural gas fuel and an electric circulation pump. But I'm open to suggestions for more cost-effective systems.)

"Financial comparisons clearly demand data. Similarly when the location is given we must expect that information about the conditions in that region can be used."

OK. I approve of you using the location and doing with it what you will. I like the responses that approach engenders. It's not wrong. No argument. If you think we "must expect", then go ahead and expect, and produce that result (which you have).

Now, supposing that the reason the location was given was to show that there are a variety of seasonal temperatures throughout the year (not just 'winter' and 'summer'), and suppose that you were to exclusively consider this challenge on the only actual 'location' given: only and exclusively inside a building kept at 21^o and the financial comparisons: "60 19-in. CRT monitors [being replaced with] 17-in. LCDs." is ALL you get to go on. How do you decide the financial benefits without imputing external data?

That's the other approach to this challenge. Can you think of a way to a clear response using just the data given?

Understandably, given that you have already spent considerable time and thought in producing the response you have, you may be unwilling to try the challenge from that point of departure. Whether you are or not, your original response was fine with me, and you may, with my blessings, defend it as the only approach if you wish, especially considering how much you enjoyed the process . ('course, you don't need my blessings! But you can have 'em anyway. )

Mark

"I think you know what I posted. (But just in case, the contribution of the CRT's to summer cooling is to raise the cost of it. So yes, I really mean my 'apparent implication' that CRTs contribute to summer cooling."
I wasn't sure, so I was giving you the benefit of the doubt. It is entirely untrue - all the energy that is supplied to a CRT ends up as heat, though you may initially feel slightly cooler when you first switch the CRT on - because it has a fan that moves the air.

"Not sure if this part of the question is intended for me. Did I say somewhere that I don't support the possibility that there are cheaper sources of heat than electricity?"
No, but this isn't the only posting of yours that supports a posting whose conclusion depends on such an assumption.

"My own favourite --in terms of bang for the buck-- is closed-system hot water radiators with natural gas fuel and an electric circulation pump. But I'm open to suggestions for more cost-effective systems."The economics of natural gas depend on location and availability. If I was located in one of the Canadian hydro-electric regions, I would probably look favourably at heat pumps (air conditioning run so that it cools the outside world and heats the interior). I'm not certain whether this applies to Torono. I used to use natural gas, but have now largely changed over to wood stoves (ready availability of managed timber waste material around here). Corn-stoves (using the waste material) is another sensible route where the material is readily available.

"How do you decide the financial benefits without imputing external data?"
I wouldn't even try, as it is not reasonable to expect to do this.
Some of that "external data" is stuff I would expect most people addressing this issue to assume - such as that 19" CRT's consume more electrical power than 17" LCDs. However, that alone is not sufficient to address the financial constraints, so you need more data. Occam (and KISS) lead to the requirement to acquire the minimum data that would allow you to address the problem. That must include the cost of the LCD display, the difference in dissipation between the LCD and the CRT. After that, we still need some indication of the energy costs that such a medium-sized company would incur. More external data (at a low level) is needed to see that in any part of the North-East USA, a constant indoor temperature in an office with CRT screens requires air conditioning, so we can assume that the savings in cold periods will at least equal the difference between supplying the energy from CRTs and supplying that same energy using heat pumps (the air conditioning units) with electricity at the same price. That needs a little basic knowledge of heat pumps (physical knowledge will give an idea, but practical units are air-conditioning units are not "ideal" heat pumps, so refinement still needs data mining). However, this same data source will provide the approximate savings when cooling is needed. As we find the savings in summer are within a factor of two of the savings in winter, we can use the average of the two - so we know our averaged errors here are less than about 30%."That's the other approach to this challenge. Can you think of a way to a clear response using just the data given?"As financial comparisons are needed, and no financial data is given, it is clear that no solution to the question as posed is possible without importing (or inventing) data.

(Occam and KISS both demand the simplest route possible. If the simplest route to answer the question requires that data be imported, these well-respected nostrums demand that this is what we do.)

"unwilling to try the challenge from that point of departure"
Is your point of departure is to try to answer the challenge it without importing data? I would not even consider it, as no useful conclusions can be drawn.
I think that constitutes a robust (and not in my view overly robust) verbal defence of the view that the question as posed cannot be answered without importing data. But it requires factual support, as follows:
Even if we allow general knowledge of physics and of the operation of CRT and LCD screens, the most we can say is that the screens that consume lower power will never be more costly in terms of purchased energy than the screens that consume more power (unless the facilities manager of the company does something completely stupid). The next stage of imported knowledge is that 19" CRTs consume more power than LCD screens, and that the temperature in all parts of the North-East USA goes above 70^O F for at least part of the year - so we know that air conditioning is required. That (and the modicum of physics knowledge already assumed) tells us only that some savings in total power consumption are definitely possible. So, we've imported data, but still need more to answer the question as posed.

Even that is not true, unless you live somewhere that electricity is cheaper per kWh than all other fuels; even then it may be cheaper to use storage heaters or to run heat pumps than simply use daytime electricity for resistive heating (or its equivalent).

...

Approximately 271.2 days

60[(19/17 X 365)-(17/19 X 365)]

Mark

By assuming that the cost recuperation could be calculated using the accounting practice of yearly book-keeping, I think that

60[(19/17 X 365)-(17/19 X 365)] = 271.2/365 days was too arbitrary.

Perhaps a fairer comparison of the sizes of the monitors as the only indicator of their difference in usage might have been

60[(19/17x)-(17/19x)] = 13.3746/x days,

where x is the number of days of normal use calculation (by the accountants) for both varieties of machine,

might have given more opening to acceptance of the variety of the ambient conditions without regarding a heat exchange with no actual data.

Hey! It's past September 2nd. Where's the answer to this challenge?

Mark

There is about a 50 watt difference between the monitors. If the heating requirements are over 50 watts, the savings are zero. If the cooling requirements are over 50 watts the savings are 50 watts plus 20 watts or so to get rid of the 50 watts of heat. In the northeast, we heat at least 50 % of the time, savings zero. Let's say 25% of the time we neither heat nor cool (50 watts savings) and 25% we cool (70W savings). Therefore, year-round we save 30 watts. The work year is 2080 hrs x .030 kilowatts = 62 KWH x $.12/KWH = 7.49/ yr. Let's assume we can get the new monitors for $100 each, delivered, installed, and configured. Further assume that the cost of money for this company is 8% (fairly typical today). We would lose about $.50/yr forever. So the time to pay off the new monitors is forever, eternal, and infinity.

Hi, kkayser!

A great big welcome to the CR4 crew! And what a great question you have chosen to chime in upon!

Hope to see lots more of you around these here parts. Your answer provides us with a freath of bresh air in its approach.

You might consider using the 'postulation' and 'beauty' marks that I have now suggested ought to be applied in responses... only to this challenge so far...nowhere else in CR4, more's the pity!

Mark

Fools there is plenty of data, it is called fudge factor or hippie mathmatics, or al gore maths for wanna be presidents, first ya start by decribing the cost benefits to the penguins, explain how you will need 2.5 million to probably study the power savings by hiring unknown specialist in monitor breakdowns in the earths crust as land fill, third come up with unrealistic figures that the new monitors not only produce electricty they also increase the pengiuns ability to cool themselves down !!! Hence finish ya report of that is 400-500 pages long that no one will want to even get past page 6 bingo you are now and enviormentialist and ya only needed 2.5 million to prove PS ya will need to travel to antartic for happy snaps with a baby penguin to justify it!

There are a lot of factors being examined in this equation. Productivity was one of them, but missed out on the fact that a change would be seen as a positive and increase productivity even with a smaller screen. There is also the health factors that are not listed or accounted for, but the question at hand is related to energy savings to pay for the monitors that are being replaced.

To solve the problem you would need the difference in power of the two monitor types, the cost of energy, and the cost of the monitor.

You can factor in the environmentals but you would have to take into account the degree heating days and cooling days. If they are roughly even then it could ne factored out, but you would also have to take into account differences between energy types used for heating versus cooling.

Utlimately you need to know what upper management wants to hear and how deep they want to go into, and if there is a vp looking to undercut your stance. They will use the buzz words like TCO, so that is were you may want to start.

Me, I just like the flat panel display because it frees up almost 2 square feet of desk space for me to accumulate more crap that needs to age until it goes bad and can be tossed out!!!

I would guess never as any savings in power consumption would outweighed by the extra demand on the heating system... Could it be that simple?

Hi, Lemmy70!

Perhaps. Depends upon the cost of reciprocal demand for cooling due to lack of CRT participation in cooling demand during the summer. And the rising cost of electricity.

Mark