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Heat Pumps BTU Production Inquiry

12/31/2019 4:15 AM

In the current issue of Texas Co-op Power, there is an article on heat pumps. It states “The U. S. Department of Energy states that heat pumps can produce 1.5 to 3 times more heat energy than the electrical energy it consumes”. How does the BTU that goes to heat the furnace, to make the steam, to turn the generator, to the distribution system, and to the heat pump produce more heat than just using that BTU in a furnace? I believe the heat pump uses a lot more BTUs than a furnace would. Aren’t we supposed to conserve BTUs?

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#1

Re: Heat Pumps

12/31/2019 4:33 AM

..."The main difference between a heat pump and a resistance heater is simple. An air source heat pump transfers heat, while a resistance heater creates heat. The reason that heat pumps are more efficient? Transferring heat is more energy efficient than creating heat."...

https://kobiecomplete.com/blog/3-reasons-why-a-heat-pump-is-the-best-heating-system-for-your-florida-home/

Of course there are other factors to consider, with a heat pump you need a second stage heat that's usually electric because the heat pump doesn't really cut it below freezing temperatures outside...and the heat pumps are more expensive initially...but if you go outside and check the amp draw on your compressor vs a 10kw heatstrip, you can see right away that the compressor draws considerably less amperage...probably less than half...

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#2
In reply to #1

Re: Heat Pumps

12/31/2019 5:53 AM

But which uses the most fuel? The furnace or the heat pump?

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#3
In reply to #2

Re: Heat Pumps

12/31/2019 6:11 AM

The furnace will use more fuel typically. The furnace burns fuel. The heat pump uses electricity typically.

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#5
In reply to #3

Re: Heat Pumps

12/31/2019 6:42 AM

Doesn't the electricity come from fuel?

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#6
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Re: Heat Pumps

12/31/2019 6:52 AM

Not necessarily...Reducing the heat load is more important than heating type anyway...

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#7
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Re: Heat Pumps

12/31/2019 8:11 AM

It's not the heat load. It's the total amount of fuel required to heat by heat pump or furnace with the same amount of heat to warm the same area.

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#8
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Re: Heat Pumps

12/31/2019 8:25 AM

Yeah I get what you're saying, but what I'm saying is that the most efficient means of heating a house is to reduce the heat load, that has the potential to save more money no matter what type of fuel you are using to heat the house...Insulate to save money...

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#9
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Re: Heat Pumps

12/31/2019 8:45 AM

No matter how much or efficient the insulation is, it's still going to need to be heated. So, which uses the less total fuel, heat pump or furnace for the same amount of space to be heated?

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#11
In reply to #9

Re: Heat Pumps

12/31/2019 12:10 PM

Generally a heat pump will use less fuel.

Heat pumps can and do often operate with COP above 3.0 and sometimes even above 4.0. This means 3 or 4 times as much heat is being moved than the energy used.

For natural gas power plants, efficiency of electricity delivered to fuel burned with line losses is probably between 35% and 55%.

This means that a heat pump delivering the same heat as a fuel powered furnace will typically result in less fuel burned even before considering things like cost of fuel delivery.

There are of course limits. When it is very cold outside heat pumps don't work as well, so it is a good idea to have supplemental heat if you live in places that get bitter cold.

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#12
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Re: Heat Pumps

12/31/2019 12:42 PM

It seems like the heat pump is a perpetual motion machine. You get more energy out than you put in. No. The efficiency that is defined is based on electrical energy. The total energy is not figured in. Just another way to sell things. More coal or natural gas must be produced to get the heat from a heat pump than what would be obtained by burning it in a furnace. If the goal is to use less hydrocarbons, then use a furnace instead of a heat pump.

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#13
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Re: Heat Pumps

12/31/2019 1:43 PM

A heat pump is not a perpetual motion machine and I would recommend that you do some research on what a heat pump does and doesn't do if you haven't already.

To give you the cliff notes, a heat pump moves heat from typically underground into your house. It uses electricity to pump this heat, it is basically an air conditioner working in reverse.

The ground temperature below 6 foot is much more consistent year round than air temperature. An average of around 50 deg F depending on location and time of year.

You can move that heat with a pump and heat the intended space above the 50 deg F. Think of how an AC can cool a room despite it being hot out. You are also cooling the ground but it is a large heat well. Conversely you can use that same heat pump to pump heat into the ground and cool your living space in warmer weather.

Basically the ground becomes a heat storage vessel. You are using electricity to pump the heat into and out of the ground as you need it. No magic or perpetual motion involved.

This process doesn't work as well when the temperature is really cold out because the ground gets colder and you need supplemental heat.

As others have said a furnace or electric heater uses fuel to create heat often from combustion instead of moving it and is a completely different process.

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#14
In reply to #13

Re: Heat Pumps

12/31/2019 1:54 PM

You are way off. You're talking about geothermal. That's completely different than my subject. Maybe you need to look up the difference between an air conditioner heat pump and a geothermal pump.

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#15
In reply to #14

Re: Heat Pumps

12/31/2019 2:28 PM

Geothermal aka ground source heat pumps, but there are air source heat pumps which is what I am guess you mean. They work on a similar principle which someone provided an article link to. In that case the air is used as the basis and in Florida for heating this probably works well since it doesn't often get that cold. The idea of both is that you move heat instead of burning something which others have stated.

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#19
In reply to #14

Re: Heat Pumps

01/01/2020 2:29 AM

Whatever you are smoking, I want some.

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#16
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Re: Heat Pumps

12/31/2019 2:54 PM
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#17
In reply to #12

Re: Heat Pumps

12/31/2019 6:28 PM

All of that is just plain wrong.

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#31
In reply to #12

Re: Heat Pumps

01/02/2020 5:55 AM

<...It seems like the heat pump is a perpetual motion machine....>

That's nonsense.

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#18
In reply to #9

Re: Heat Pumps

12/31/2019 9:26 PM

Well if you have access to free wood, then a fireplace is the cheapest way to go...though it's not distributed evenly throughout the house...

https://www.woodheat.org/cord-wood.html

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#24
In reply to #18

Re: Heat Pumps

01/01/2020 12:55 PM

Solar heat.

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#35
In reply to #9

Re: Heat Pumps

01/03/2020 7:40 AM

A 10kw heat strip produces about 30,000 BTU.

A 30,00 BTU heat pump requires only about 10KW to move the same amount of heat from outside to inside as the heat strip does to produce the heat.

There are heat pumps that are designed to operate at lower temperatures,and the ground source slinky-coil type,buried in trenches, actually capture the latent heat when the soil freezes,so freezing soil is more efficient than 32F degree soil.

When all is said and done,the electricity required to run the heat pump is less than the electricity required to generate the heat on site.

Consider this for instance: A 10kw(30,000 BTU) heat strip consumes approximately 45.5 amps at 220 volts.

A heat pump moving the same number of BTU's will require approximately 13.6 amps.

It does not matter how the required KW are generated,the delivery cost to the end user is the same.

The heat pump requires less demand from the power plant, no matter the type;solar,wind,nuclear,etc.

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#10
In reply to #5

Re: Heat Pumps

12/31/2019 10:26 AM

Electricity comes from a generator which is driven by a turbine which uses hot gasses from burning fuel or steam generated in a boiler using fuel...but if you try to use fuel in most heat pumps, not much good will come of it.

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#4
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Re: Heat Pumps

12/31/2019 6:38 AM

..."Heat Pump systems operate on electricity and are ideal for homes in moderate climates. ... In most areas, electricity rates are lower than natural gas, meaning that a heat pump system will cost less to operate than a gas fired furnace. *Quietness. Hot air heat pumps do not make as much noise as a furnace."...

http://www.airmasterheatingandair.com/what-are-the-pros-and-cons-of-a-heat-pump-vs-a-gas-furnace.html

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#20

Re: Heat Pumps BTU Production Inquiry

01/01/2020 4:53 AM

Air source heat pumps are capable of heating a house, even when the air temperature is down to -20°C, when they are designed for those temperatures.

The COP is much better when the air is warmer, but it can still be more efficient than electric resistance heating, typically 1.2.

In Sweden, most houses are heated by heat pumps, the majority are air source. The costs of getting a borehole drilled to 150+ metres down can outweigh the benefit of higher COP during the winter months.

A ground source heat pump can achieve a COP of 3-4 all year, while an air source heat pump will manage 3-4 in mild weather (10°C+) and as little as 1.2 in the coldest conditions.

Most in the European market have resistance heating as a booster for the few days a year that the heat pump may not cope. It is usually more efficient to select a heat pump to suit normal winter conditions and have a booster for extreme weather.

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#21

Re: Heat Pumps BTU Production Inquiry

01/01/2020 7:37 AM

Think of a heat pump as a big refrigerator that you can run normally in the summer and backwards in the winter. When you compress a gas or liquid it gets hotter. When you expand a liquid or gas it gets colder. Just as water always seeks a to balance it's level with all the other water around it, anything hotter than its surroundings cools down and anything colder than it's surroundings heats up. So in a refrigerator you compress a liquid on the outside, the heat this makes is lost to the air surrounding the fridge. Then you pump the compressed liquid to the inside and allow it to expand. It goes colder and in an attempt to balance it's temperature to the surroundings it sucks heat out of the air/food inside the fridge. The liquid goes round in a continuous loop with some of it always being compressed and losing heat to the outside and some of it always expanding and sucking heat from the inside. You can run the thing backwards so that the liquid expands and sucks in heat on the outside and compresses so loses heat to the inside. The amount of energy needed pump the liquid around the loop and compress it is less than the amount you would need to burn in fuel to get the same heating effect inside your house, mainly because furnaces are inefficient and a lot of the heat they generate goes up the flue with the waste gasses. My home furnace has a flue made up of two concentric pipes. The air into the furnace is sucked down the outer pipe and recovers some of the waste heat going up the inner pipe with the exhaust gasses. The intake air arrives at the furnace already partially heated so I use less gas to get it up to the temperature I want it to be.

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#22
In reply to #21

Re: Heat Pumps BTU Production Inquiry

01/01/2020 10:31 AM

My take is a bit less complicated to understand; Recall that we are talking about a Heat PUMP, the machine literally moves heat from place to place, it does not generate the heat it is moving. Just like a pump moving gasoline from a tank to a car, a heat pump moves energy from a source to a user. The energy of the gasoline being pumped is not created by the pump. In this analogy the COP of the gasoline pump would be the electrical energy input to the gasoline pump as a fraction of the total energy embodied in the gasoline delivered.

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#23
In reply to #22

Re: Heat Pumps BTU Production Inquiry

01/01/2020 10:56 AM

There seems to be some confusion about the heat pump. The heat pump that I am referring to is the compressor type. Basically, the exhaust from an air conditioner. The geothermal heat pump is completely different and I'm not referring to it. What I want to know is how many btus or calories that it takes to produce a btu or calorie of heat out of the heat pump. The btu heats the water to steam, steam drives the turbine that drives the generator that makes the electrical power. It is sent to the heat pump to drive the compressor and fan. During all these processes, the amount of that btu gets smaller and smaller. It will be very small by the time it gets to the heat pump compressor. How many btus does it take to get a btu out of the heat pump starting from the boiler furnace?

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#25
In reply to #23

Re: Heat Pumps BTU Production Inquiry

01/01/2020 2:53 PM

..." Coefficient of Performance (COP) is the most common measurement used to rate heat pump efficiency. COP is the ratio of the heat pump's BTU heat output to the BTU electrical input. Conventional electric resistance heaters have a COP of 1.0 meaning it takes one watt of electricity to deliver the heat equivalent of one watt. Air-source heat pumps generally have COPs of 2 to 4, meaning they deliver 2 to 4 times more energy than they consume. Water and ground-source heat pumps normally have even higher COPs of 3 to 5."...

http://c03.apogee.net/mvc/home/hes/land/el?utilityname=wrecc&spc=hel&id=2312

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#26
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Re: Heat Pumps BTU Production Inquiry

01/01/2020 3:02 PM

I want it from the boiler.

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#27
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Re: Heat Pumps BTU Production Inquiry

01/01/2020 3:16 PM

They both are using the same electricity....but it is probably cheaper on an energy cost level, to deliver gas per therm than the electrical equivalent...so they probably come out about the same...

https://www.centerpointenergy.com/en-us/Services/Pages/natural-gas-electricity-cost-comparison.aspx?sa=mn&au=bus

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#28
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Re: Heat Pumps BTU Production Inquiry

01/01/2020 3:34 PM

The gas costs half as much, but you use twice as much, itsa wash....I prefer electric heat strips because they are simple, low maintenance, easy to fix when something goes wrong...KISS

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#29
In reply to #26

Re: Heat Pumps BTU Production Inquiry

01/01/2020 5:34 PM

Reread post #11.

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#30
In reply to #26

Re: Heat Pumps BTU Production Inquiry

01/01/2020 11:53 PM

If you want to look at the system from the fuel generating the electricity through to the warm air entering the home then I think this might be a way:

A typical figure for boiler efficiency is 30%, for generator efficiency about 90%, for transmission efficiency about 95%. Putting all these together to get from BTUs in the original fuel to KW at the heat pump gives about 25% efficiency. If the COP on the heat pump is around 3.5 then the system as a whole works at 90%. This means that for every BTU in the gas or oil or coal at the generating station you are getting 0.9 BTU of warm air at the discharge of the heat pump.

If you want to compare this to, say, using the gas directly in a home furnace then the furnace efficiency is about 30% also so each BTU in the gas gas would give you about 0.3 BTU of warm air.

What is interesting is that if you use hydro to generate the electricity the efficiency is about 80% giving a net efficiency to the heat pump of 76% and an output from the heat pump of 2.66 BTU for every BTU in the falling water. In this case, using the electricty directly to heat the air would only give you 0.76 BTU.

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#32
In reply to #30

Re: Heat Pumps BTU Production Inquiry

01/02/2020 5:58 AM

efficiency effectiveness

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#33
In reply to #30

Re: Heat Pumps BTU Production Inquiry

01/02/2020 8:56 PM

Sargasso,

You are way off when you state a home furnace efficiency of 30%. The worst of the 80-100 year old furnaces had efficiencies of 40-50%, and typical cheap furnaces are about 80%. The best furnaces that condense the water from the exhaust gases are about 94-96% efficient. With any furnace, the size of the flue pipe tells you about the efficiency--very efficient condensing furnaces have 2" PVC pipe, while the really old ones had flue pipes of 8" or more.

Now, Papadoc is asking about the overall system efficiency, starting with natural gas as the energy source and the home as the energy user. A combined cycle gas fired generating plant has a net efficiency of around 55% but can be a little higher, while a typical steam/boiler system has an efficiency of close to 35% (the rest is split about evenly between the flue and the cooling tower). Next, comes transmission of the electricity to the user, and I will allow this to be around 90% efficient (only 10% loss). Then we have the efficiency of the heat pump (air source as Papadoc has clearly stated). This efficiency is the heat pump's coefficient of performance (COP) and ranges from 2 to 3. Since Papadoc is in Texas, I will assume a seasonal average COP of 2.5 (250% efficient in moving heat from the outside to the inside). Multiply these together to get 0.55 x 0.9 x 2.5 = 1.24 which is a net gain in energy. If the heat pump's COP is only 2, then the system efficiency drops to 0.99.

For the gas furnace we have to also allow transmission losses, and I will assume 95% efficiency (or 5% loss), with these losses being pumping costs and gas leakage. Putting the numbers together we get 0.95 x 0.94 = 0.89.

Anyone can play around with the assumptions behind these numbers and find that a gas furnace is more efficient or a heat pump is more efficient. However, one other detail is getting ignored--the seasonal changes in the electric utility's generating plant equipment loads. In Texas and most of the temperate areas of the USA the electric utility must have enough equipment ready to operate to meet its peak demand, which occurs in summer near the late afternoon. By adding heat pumps (or for that matter, electric resistance heating) the winter load is increased and the utility will bless you with a lower rate for the heating system because their equipment is getting a more even seasonal load.

--JMM

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#36
In reply to #33

Re: Heat Pumps BTU Production Inquiry

01/03/2020 1:22 PM

Dear JMueller,

Thanks for the update. I will take your efficiency numbers as correct even though I suspect they may be from the furnace makers......

I think Papadoc was looking for the overall picture and this is pretty clear from your reply.

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#37

Re: Heat Pumps BTU Production Inquiry

01/03/2020 2:44 PM

IF you could develop a process to convert the heat directly to electricity at a very high efficiency,you could have a perpetual motion machine,which would violate the basic laws of physics.But then again,laws are meant to be broken....

If you used a condensing type boiler that uses the latent heat from the water vapor that goes out the exhaust for your heat the total carbon footprint of the heat would be reduced,disregarding cost.

Many years ago Lennox had a pulse combustion boiler that exploded the gas in a chamber and used a PVC exhaust pipe.It was over 90% efficient.

This was the same method that the German "Buzz bombers" V2 rockets used.

The opening and closing of the air valve and combustion created a buzz that could be heard from a long distance.

Older style boilers used small chunks of coal on a ember bed to produce steam for the generators.

Now,the coal is crushed into a fine powder,and burns more efficiently.

Fossil fuel generating stations are getting more and more efficient all the time,and there is an economy of scale involved;large boilers are more efficient.

Solar energy is being added to the grid at a furious rate and it will continue to be a supplement to the other sources of energy.Solar cell efficiency is also being improved constantly.

IF you are sourcing your electricity from the same place,it is more efficient for the energy provider to send less watts(Amps X Volts) to your house,regardless of what you are using them for.

There are heat pumps that use gas as an auxiliary heat source instead of heat strips,but you will still generate a bigger carbon footprint than using a heat pump.

I presume you are really interested in the lowest carbon footprint of the energy?

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#44
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Re: Heat Pumps BTU Production Inquiry

01/07/2020 12:05 PM

If an AC was installed in a wall that separates two rooms of equal dimensions and insulation with no additional air in and no air out and the AC is turned on and the ambient temperature of both rooms is 90 degrees F, what temperature would each room reach before stabilizing? What if the ambient temperature of both rooms is 40 degrees F?

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#45
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Re: Heat Pumps BTU Production Inquiry

01/07/2020 1:16 PM

Given enough time,the rooms will reach equilibrium at a higher temperature than 90F.,and continue to rise until the temperature reaches a higher temperature than the hot gas,higher because system inefficiencies add to the heat.

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#46
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Re: Heat Pumps BTU Production Inquiry

01/07/2020 3:54 PM

There isn't enough information to answer the question.

Size of the rooms, size of the Air conditioner. how well insulated etc

Obviously one room will become hotter and one room colder.

The total thermal energy input to the two rooms combined will be roughly 3400 BTUs per kWh of electricity consumed.

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#38

Re: Heat Pumps BTU Production Inquiry

01/04/2020 1:27 PM

“The U. S. Department of Energy states that heat pumps can produce 1.5 to 3 times more heat energy than the electrical energy it consumes”

The problem with this statement is the word "produce". Air source heat pumps do not produce "heat energy" or thermal energy. They simply take heat from the outside air and move it inside.

If an heat pump is putting out 2 times more thermal energy than it is consuming in electrical energy, It just means it is taking the extra energy from the heat in the outside air.

That energy happens to be free and readily available in climates like Texas. There is no magic here, no smoke and mirrors, and no perpetual motion machine.

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#39
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Re: Heat Pumps BTU Production Inquiry

01/05/2020 12:08 AM

...that being said the cost of ownership should be mentioned...heat pumps are complicated, expensive, a pain in the arse to troubleshoot and repair...and any furnace worth it's salt will outlast any heat pump, require less repairs, are easy to troubleshoot, and usually somewhat easy to repair, though it can be expensive at times...Electric heat strips rarely fail and last a long time, are easy to repair, easy to troubleshoot...Gas furnaces supply hotter air than heat pumps, electric resistance heat supplies hotter air than heat pumps, but not as hot as a furnace...Up north I would go with a furnace, in the mid region, say Carolina's, Georgia, I would go with a 2-stage heat pump...and in the south, electric resistance heat....

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#40
In reply to #39

Re: Heat Pumps BTU Production Inquiry

01/05/2020 10:50 AM

Impeccable logic; though I disagree about the furnace.

The situation summarizes perfectly why a carbon tax is soooo necessary to put more of the unseen costs back into the furnace based system.

Heat pumps for reverse cycle, ground source, solar assist or in co-generation or hybrid systems are pretty new as consumer technology goes. Sure A/C has been around a while but the controls and the high-efficiency compressors using modern refrigerants make the A/C systems, even of the 1900's, look pretty dark ages in terms of their total system tech when compared to today.

As time goes on and more complex systems become more common costs will drop, reliability will improve and the skills of the support technicians will also so the maintenance factor will become less of a cost burden. In the meantime, choosing the right system and the right supplier and installer is a non-trivial design choice.

If your birthdate is early enough you might have seen this scenario unfold before a few times; Autos, telephones, computers, TV and internet are all consumer technologies that are almost inconceivably more complex now than they were as little as 10 or 15 years ago, much less 30 or 50 years ago. Now that the market is starting to drive things energy toward higher performance and higher integration in home energy use, similar things will happen and oil and gas furnaces will become the rotary phones, TRS-80's and CRT TVs of the next era.

A gas furnace may be the cheapest way to keep your living room warm next winter in the northern tier but if you are making an investment with a longer time horizon it is not so wise. For home owners of even modest means, a bank loan or adding to a mortgage to finance a more efficient (and lower carbon) solution will likely have lower lifetime cost and much higher resale value.

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#41
In reply to #40

Re: Heat Pumps BTU Production Inquiry

01/05/2020 2:09 PM

That's just not realistic....Gas is still growing and will be around for hundreds if not thousands of years as a major energy source...If you think the skill level of technicians is improving, you're not in the business...The last thing we need is any more taxing schemes to rob the people...

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#42

Re: Heat Pumps BTU Production Inquiry

01/07/2020 11:16 AM

Heat pumps, ground fed, replace running power costs with initial installment costs.

Kilometers of tubing must be buried 2 meters deep to provide a stable heat sink/source of approximately 12 degrees C.

A water bearing substance is pumped through the tubing and fed to heat exchangers in the dwelling. The water is now at 12 degrees C

A simple cooling arrangement, with potentially greater than a 4 energy index, pumps the water through a radiator in the dwelling that is inserted into a forced air ducting system.

The electricity is used to pump the water through the tubing and move the air through the radiator only.

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#43
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Re: Heat Pumps BTU Production Inquiry

01/07/2020 11:56 AM

This discussion is about AC heat pumps-not geothermal heat pumps. Geothermal pumps are completely different.

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