Air Conditioning Requirements for Zone 1

I don't have too much to offer as far as calculations go, but I would ask if you have checked the A-Coil for blockage? I've seen A-Coils gets pretty gunked up, especially if any previous home-owner was hair-brained enough to run the system with no filter in place.

I've got about the same square footage as you, in the mid-west, and get by with a 3T unit, I have less windows, and very little shade. I would imagine you have a lot higher humidity to deal with. Is there any chance the A-Coil is freezing up?

Tom D.

Your calculation gives you 63,000, that answer is in BTUs per hour.

One site I've looked at gives a conversion of 12,000 BTU to 1ton A/C

http://wiki.answers.com/Q/How_many_BTU_per_Hour_equals_1_Ton_of_Air_Conditioning

Wikipedia confirms this.

http://en.wikipedia.org/wiki/Air_conditioner#Equipment_capacity

But other sites give lower estimates of the BTU requirements.

http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized

Nearly all the sites refer to square feet of building space, but clearly the height of the rooms is going to matter so cubic feet might give a better estimate.

A good and easy rule of thumb is 1 ton per bedroom, 3 bdrm house = 3 ton unit...then add and subtract for extra rooms, vaulted ceilings etc....in any case your system sounds like it is properly sized to me...I would check filter and evaporator coil, as these are the most common problems....Evaporator coils need to be cleaned periodically according to usage and environment...This involves removal of the coil and generally runs $4 to $500....But this is a job for a professional service mechanic, as is the diagnosis...

What you have sounds fine, compared to what I have in AZ, except we don't have the humidity you have by the ocean.

What's the RH inside your house on a hot afternoon?

What's the duty cycyle of the system on a hot afternoon?

usually in the high 60's to low 80's

the RX15 Trane unit runs for 2 hours or so in between cycles , set on 78F with an outside temp of 92-96. Too long it seems.

The unit is 3 yeasr old and I change filters religiously.

Thanks for any input

Thank you for the information. I'll give that a try this week end.

People often do not bother to seal houses in warm climates. This results in a high number of total air changes per day. Each houseful of cooled air escapes and is replaced by a houseful of warm and humid external air.

Pay careful attention to the sealing of the house. Stop all holes, cracks and crevices.

The house also must be well insulated.

Think of the house as a balloon you are inflating - where does the air go to stop this. Warm climate houses are virtual sieves.

Professionals can tel the number of air changes per day with trace gasses, but I do not know how this is done.

summer is here.

That back door is opened 25 odd times each day with the grand kids coming in and out.

could those brief openings cause such trouble??

After studying what you described, I am not qulaified to even attempt some of that.

The unit coils outside are clean, but if I knew what solution to use, I'd clean them off again just to be sure.

I do not know if i can get to see the coils in the unit , in the unit part in the attic ( plenum and such).

As for the gauges, I am not going to try that but will call someone who is qualified and suggest they have a look at exactly that.

thank you for the suggestions. AC is way outside my range of workmanship. thank you again.

Dear Sir!!

Would recomend some simple tests (if not stated till now...)

1)Please measure the aircool on the blower outlet;it has to be 2-4 Celsius!(Not less!)

-ofcourse see the outlet is not clogged or weak flow (presumably you checked it)

If the temperature is as perscribed - the cooling unit is OK !!

2)Check your ceiling and walls temp. by hand touch!!

- if in the midday and while AC working , you feel it is hot,it means one thing

Your insulation is inadequate...

Vents are 3 years old.... all replaced.....good air flow but I will check temp.

Ceiling is not hot at all even at noon time temps of 94-96 F.

did you say 2-4 C temp at the vent? That is around 39F. Correct? I will measure that.

Thank you.

Three tons would have been enough for this house in Orlando.

I agree with the other replys to check the evaporator for lint and fungus and the temp rise at the condenser.

The "Duh question" though is; how is the air flow at the vents? Is the blower clean and the belt tight/in good shspe?

The whole unit is 3 years old.

I regularly change filters.

Air comes forcefully through the duct work as that is also only 3 years old.

windows are new.

14" of insulation.

Tyvek wrapped outside and then vinyl siding.

I am just at a loss as to why this big unit is not cooling better.

I am NOT qualified to look into all the areas suggested. I decided not to try and dig into the unit in the attic .

Looks like this will have to be trusted to an AC guy....hopefully the one that comes is honest and knowledgeable. the folks who sold me the Trane XR15 have clsoed shop a year ago.

Thank everybody for their input.

Good air flow.

would not have a clue as where the 'belts' are on this thing.

Thank you for the input.

Found a nice, short .pdf "The Principles of Air Conditioning" that has some good diagrams, as well as some checklists that could help you do some of the checks that have been mentioned. One poster said that the air coming out of the vents should be a certain temp, but that's a bit misleading. What really matters is the differential temperature before and after the A-coil. That is a quick and easy check, provided you can get to the inside unit. You measure the return air temp, then the air that is exiting the A-coil. The .pdf says you should see 15-20 degrees (F) difference (see page 23). With my fairly new 13 SEER unit, I would get 23 deg difference regularly.

You mentioned that that unit was in the attic, which may mean it's a "down-flow" unit. Basically, when you look at the diagrams, the flow is reversed, as are the blower and A-coil. I have seen attic mounted units run conventionally too, with the return at the bottom, and the outlet up top. Just something to keep in mind as you look at the diagrams in the booklet. Here's a link to the PDF:

LINK

You'll be an A/C expert in no time :)

Tom

TD,

Thank you for locating this. I am by no means looking to be an expert in AC..... too hot this time of year and the clientelle is too aggravated when it breaks!

Thank you.

You know..........just for the hell of it, could someone dig up a really good picture ( schematic, drawing) of what the inside of both the outside and inside units look like for a central AC unit.

I do not what a inside coil or condenser coil would even look like. I can get my ahnds on some of the unit in the attic with little trouble.... and could look for lint, hair, fungus, etc IF i knew where to look.

Thank you all for anything in this nature.

Just a thought. If your grand kids are constantly going in and out of the house, is there an interior door that could be closed to restrict the hot or warm outside air in the room where the exterior door is located. My son goes in and out, in and out, and the warm air entering the house plays havoc with the A/C in keeping the house cool. I finally ended up installing a bi-fold door in the room where the exterior door is located to restrict the hot outside air to the one room with the exterior door. That seemed to help my situation substantially in keeping the rest of the house cool.

That is exactly what I am seeing.

We have one big ,front room with TV and kitchen combined. The rest of the house is cool. The laundry room with both washer and dryer is freezing!

The front room never cools down.

Answer may be as simple as send the grand kids back to their parents ha ha !

Thanks for sharing that. It may take me some thought as to how to put an enclosure on that back porch where everybody comes in at...something to maybe slow down or keep out some of the heat.

Really funny thing is that just a few years ago we never had a central Ac or heat. we used fans in the summer and a wood burning stove for winter. Summer was hot and we had one window AC for at night.

Got sick and everything changed. Now I spend mornings and nights working and most of the hot afternoons inside the house.

Thank you for the insight into your situation .

The rest of the house is cool. The laundry room with both washer and dryer is freezing!

Turn off the vents to the laundry room. That will give more cool air to the living room. Intake vents could be a factor. Make sure they are clear of blockage in the living room and kitchen, but block them in rooms you don't want to cool, and close the doors of those rooms.

In the 3 years that you have owned this did it ever work satisfactorily?

Can you quantify the "good" readings on the gauges please? (compressor running)

Wal,

I work outside almost all day. My shop is very hot as we just have big fans blowing. I really never noticed much until this year when I fell sick and had to spend more of my time inside the house.

I feel that the unit never did cut on and cut off in a timely fashion. It ran for hours during the afternoon heat and cut on and off only at night

This summer is the first summer we have a new roof, new windows and the 14" of blown insulation.

The comments by others about heat exchange caused by doors constantly being opned and shut rings a bell for me. The grand kids are always in and out.

Thank you for the input.

Open doors and aircons don't mix too good.

Do you have zones in your home that can be independently cooled?

I live in the tropics. I rely on passive ventilation in most of the house and only aircon one room at a time and only when the room is occupied or in use and we really want it very cool. Doors and windows closed and sealed.

Commercial aircon is another story.

What were the actual readings on those gauges? If you don't know how to interpret the gauges then post some clear photos.

i know what you are saying. I worked in India for some time....

inland , east of the Ghats it could be 110 F but the humidity was nil and i was comfortable at night with just the ceiling fans and open windows ( with screens, as I have never seen such large insects).

Down near Tamil Nadu on the coast it was the same but high humidity like here.....a nice AC cooled room was always appreciated when we were back in from the water.

When the winds were right, either place was comfortable for me.

I was told by someone else a long time back when we just a single window unit that larger AC units could be too big for some rooms and casue more trouble than they cure.

After reading all of your very detailed and easily understood information, I am thinking we may have one big ol' unit when we should have two smaller ones..... a suggestion made by the guy that installed this unit, but he did not really force the issue and in the end just said he would put this one.

Hell, before I got sick i was happy with high cfm output fans!

Thank you a lot for taking the time.

That is not the way. Manual J from www.acca.org is the industry and the ANSI standard for residential load calculation.

It takes in to account, insulation value,window type and orientation, number of people,wall and window area,ceiling area, etc., etc..

That said you could go to the Rheem website , they have a so,so calculation, that will get you in the ball park.

Where are you located, can you provide insulation value,widow types?

Typically homes are over sized not under sized, so you may have other issues, duct leakage, air flow too low, incorrect refrigerant charge, etc..

This house has been remodeled at least 4 times and now its on its fifth time. Storm damage has over the past 30 odd years has racked it, sacked it and even moved it off its foundation a itty bit. I spent all of last year and some of this re doing the entire outside as leak proof as possible BUT it is still an old frame house. I'll bet i have leaks some where.

I will look at the web site you provided also....thank you.

The ole Air conditioning unit, Should at its very best drop the temp. around 20 degrees from intake to first out put loover. 80 degrees in and somewhere close to 60 degrees out put. bear in mind the age of the unit and the distant you take the output Air Temp. If the large line coming from the inside coil is sweating, the ole unit is doing its best. The unit must be able to cycle on and off with no visible ice anywhere. This said and done look elsewhere, location of control. Broke ducting, return air from outside, and covering for the windows. If it ain't broke don't fix it..Find where the heat is coming from. Put a flyer on all the loovers to check air flow. Cold air will not turn corners good cirulation mean a lot..Temp. in one room may be 50 degrees but in another 80.

......huh....some of my ductwork has some really odd angles in it to get around the additions we have constantly put on this old frame house ( we cut into that roof at least 4 different times)....could need to maybe look at re-running some of those.

Thanks for that suggestion.

The only way to accurately calculate heating and cooling loads is with Manual J calculations. You really don't want to use the manual for this I used a program that I think was called HVAC Calc, it was tedious but well worth the $50

will look into it.

Thank you too.

One thing that I have found that most people miss is to take a temperature reading of the liquid line filter/dryer. If you have replaced the compressor or had some parts changed out, then there is a good chance you have contamination inside the lines that has been caught by the filter.

If you just do a simple measure of the line temp just before and after the filter and there is more than a 5 degree temp change this will tell you that there is some blockage.

I would suggest you find a contractor that will do annual maintenance, that includes cleaning coils,blower ,drain pan and drain line, plus checking the refrigerant charge. They should also check the "static pressure" of the duct system, to see if the resistance is too high to deliver the required air flow.

You can start here to find a contractor www.natex.org . Be sure to ask if they will do all that I stated, if not keep dialing.

This is typically a lower cost and more comprehensive then a service call.

• cleaning coils ( these are the ones outside and inside)?
• blower ( inside)
• drain pan and drain line (attic)
• check the refrigerant charge ( outside)
• check the "static pressure" of the duct system( inside)

Am calling this afternoon. Thank you for the time.

Thank all of you for the time. As usual, I come away with a better understanding of things I have never really noticed before.

Don't forget to insulate ductwork exposed in the attic.

• cleaning coils ( these are the ones outside and inside)?

Both. Of course, the inside ones are much harder to access. Even after you open up the A-coil enclosure, you still will have another plate/cover to remove to gain access to the blower-facing side of the coil, which is the side that is most likely to be blocked/dirty. Be careful if you do get in there, those fins are easy to bend! I have used a combination of vacuum with brush attachment, and compressed air to clean out the A-coil. There are specialty cleaners available for both inside and outside coils, the stuff for outside use is usually "stronger", because it can be completely rinsed off after application. Inside coil cleaners are usually more benign, because it's next to impossible to rinse the cleaner completely away. Tom D

Yes inside and outside coils, right on for the rest of the list.

Be aware that the inside coil can be so "impacted"(dirt deep in the coil), that it may have to be removed to be cleaned, which will add extra charges. They should be able to tell by the "static " pressure drop across the coil.

all good.

It looks like two things are impacting this situation:

the back door is always being opened...I said 25 times a day but now I am upgrading to 35 or better.

second, I think when they installed the unit, they ran some hose inside the closet, behind the fliter and up into the unit itself. All of this was sealed off and siliconed shut by me.....but i see some gap in the large hole with this tubing running from under my house, throygh the floor , through the wall and into the attic. It may be sucking some hot air from this gap. I will get some foam spray and seal that rat hole up....

Thank you all again.

The outside coils are rarely a problem...Unless they have been damaged....After reading that you have some rooms freezing and some rooms hot, you seem to have an air balance problem...If the ducts are properly installed you should have a volume control on each one in the form of a lever or phillips/slot head nylon screw....You can balance the air yourself by shutting the cold areas air volume down, until the temperature throughout the house is the same temp in every room....Do this incrementally by making a ballpark adjustment and waiting 24 hrs before re-evaluation...

.......and this would be behind the grid that shows on the outside?

I have vents that are in 3 segments. each segment can be turned down. Would this be the same?

Excellent idea...

most of them I've seen are installed in the ductwork in the attic and are little t-handles sticking out from the hard-piping. (or where the flex-duct connects to the distribution plenum)

c'est chaud..... I mean its HOT! up there...

I'll have to wait until later tonight to get up there.

Thanks for the directions.

I agree with all of that! The GA is for " those whirlybird turbine vents are for crap."

'Whirlybirds', they only look like they are working!

Yes, good idea. All of the supply registers should have some sort of dampers, face louvers, jiffy (butterfly) damper before the sa grill in the duct or OBD's (Opposable Blade Dampers) just before the outlet distributer face.

However to "Comfort balance" not properly "air balance" I would recommend opening all the dampers fully then begin the cut backs....bathrooms....laundry rooms....unused bedrooms. I actually cut back the front living spaces and dump most of the air into the master suite since that is where my wife and are are usually...........ta heck with the kids they are young.

Sealing that stuff up is a great idea for more reasons than performance and efficiency. Any air exchange with attic or crawl space air is a bad thing.

In my younger days, when I crawled through attics and under houses for an HVAC company I saw a lot of leaky duct systems. Mostly they were nuisance efficiency killers but one was an incomplete joist pan on a return air. This family was getting sick from the air being sucked in from the crawl space.

Seal it up good. Also since your duct is in the attic, adequate attic ventilation is crucial. I buried the duct and supply lines with blown insulation in my in-laws attic. The R 4.3 of the duct seemed inadequate compared to the R 30 in the ceiling. Good luck staying cool!

Thank you. well noted on the crawl spaces. I spent my youth doing the same with my old man in attics and under houses running that old Romex paper covered wire....career stopped when a spider got me and put me down for a week....

kids today have no clue as to what we went through to earn a few bucks .... no clue at all!

The age old rule of thumb is 400 sq feet per ton pluss 10% for fenestration / infiltration. Of course you can calculate it down to the nats arse, but that has gotten most Engineers close for the last 50 years.

So 1900 sq ft 5 tons minimum, with out the 10%.

400 SF per ton plus 10% IS the old way to guestimate COMMERCIAL loads (I have been doing this for over 40 years). Homes have much lower internal heat sources and occupancy rates. Commercial can have a person for every 150 SF or so, with computers and lots of lights on all day- totally different than houses (maybe 1-3 people in 1500 SF during day and 3-5 on the weekends without any lights on in the day).

CURRENT Commercial Guestimate is 350 SF per ton to allow for higher density of electronics and higher code-mandated ventilation rates.

As stated earlier, RESIDENTIAL loads are 600 SF per ton in Midwest, 500 SF per ton in South and Southwest. Highly insulated homes can run up to 700-750 SF in Midwest and 600 SF per ton in South and Southwest. There are some obvious other issues related to age of home and how tight windows are, but we are only talking about rough estimates of loads.

Yes, that is correct and I too have been doing this for 30 years but the 600 has never worked out that well since most homes leak more that commercial buildings. I have used 400 per ton between South Carolina to California and have not had a comfort complaint ever. Balance the system properly there is no short cycling of equipment just happy customers. The cost difference per ton is nominal. less rung time energy savings and room to grow. Kids leave the door or window open by accident, covered, the 600 method has always been old and too borderline of a calc.

Yes the 350 was the new guesstimate number used however with the new advancements in lighting and lighting controls and the title 24 updates the old 400 works well, though the best method for any system is the actual manual calculation.

netmaker, i didn't have time to read all the responses so If I repeat something, sorry. There are three things I would be looking at. first off, if you have air leaks in the return plenum going back to the evaporator coil you could be sucking unfiltered air into the system which could still clog up your coils. a lot of times, builders won't properly seal the return plenum and you'll have air getting sucked in through every little crack and crevice in line. Is this house two stories or one? if so, it might pay to have a HVAC guy install some electronically controlled dampers connected to a programmable timer so that you can control which rooms get cooling at what times. that way you can close off the vents upstairs during the day and close off the vents downstairs in the evening. you may also need to have the manual dampers adjusted to balance out the airflow so you are only cooling the rooms that really need it. and third, I'd think about having the roof re-decked with LP's Tech Shield (or similar) when it comes time to replace the roof, I'd also make sure you have lots of soffit vents and ridge vents and your blown in insulation hasn't blocked the soffit vents up so air can enter under the eaves travel up along the underside of the roof decking and out the ridge vents. I did that on the south facing side of my house and the difference in attic temp is probably close to 20-25 degrees F or more cooler.

ROR,

We been fixing this house now for almost two years. We put a Steel roof on just a few months back. It has a continous roof vent all across and a soffet type perforated vinyl all along underneath.

There are 4 openings in the attic walls facing out....attic vent...Just a 2x2 hole with a screen across it. The heat just bleeds out of these holes.

I have two on the two story, one the original old house itself and one on the little side room.

I then put 14" of blown Mansfield insulation ( white stuff that don;t itch).

I am still working up on the idea from a year ago to set up that big ol' shade sail over the south West part of the house.

So, what is this LP Tech Shield ? Did I miss doing something I should have?

if you have a steel roof on the house then the underside will serve as the radiant barrier but you need WAY MORE than four 2 X 2 holes. you really need a continuous vent under the eves of the roof all around, other wise the air doesn't circulate everywhere, just between the holes and the roof. (edit, just reread your response, looks like you have that but i'd bet they are clogged with insulation and plugging them up.) the heat is supposed to be coming out the top, not the bottom. if the heat is coming out at the air intakes (which is what the eve vents are) that means you don't have enough airflow. Techshield is 3/4" OSB roof decking (they used to make it in plywood too which is what is on my house before they converted to OSB which is glue and sawdust as far as I am concerned.) with aluminum foil on the backside/underside. what happens is the infrared light/energy penetrates the shingle and plywood and hits the interface between the wood and the aluminum and is reflected back out. if the aluminum is touching anything (like insulation) then instead of being reflected back out, it gets conducted on through so radiant barriers must have as little contact with the structure underneath as possible. A steel roof CAN be it's own radiant barrier if the underside is shiny metallic, but most are painted or galvanized which limits their reflectivity a lot. in that sort of situation you need as much airflow as possible (see above). they also make a zinc and aluminum filled paint that is not as good as aluminum foil but better than nothing at all that you can paint the underside of the roof with. it was developed originally to paint the interior of tanks to cut down on their heat signature and make them harder to see with night vision equipment.

OK.

I'll be in the attic this week end anyway so i will UNCOVER the insualtion that may be clogging the vinyl soffet perforated segments.

I see exactly what you mean....

The roof ridge vent is bleeding super hot air already, I think my problem may just be in spots along the attic where we got a little sloppy with the hose gun abd covered segments of the perforated vinyl.

thanks a bunch.

Storm in the GOM should cool us down the next few days...

Storm in the GOM? first I've heard about it. where and what is the expected track?