The two stage Infinity series come in whole ton sizes only. A round off to the next higher even ton size is reasonable because the unit should operate in the lower stage a good portion of the time.

Note on page 2 that the units come in 24, 36, 48, and 60 sizes corresponding to 2,3,4, and 5 tons.

http://www.manualslib.com/manual/462058/Carrier-24anb1-Infinity.html

Obviously a nice custom built home. No model numbers provided. That's not a professional quote. I would want one system downstairs and use Infinity zoning controls. Just from the info provided, I would say you are being oversized on cooling. Insist on seeing a load calculation in writing on the software letterhead. You never ever should use a HW thermostat on an Infinity system which is what you should be looking at.

IMO

Do you know what will be the R values of the spray foam insulation? If they are higher than average then you are probably very over sized with a proposal of 9 tons. It looks like the contractor is using a rule of thumb of 500 sq. feet per ton, and then rounding up for all the 2-stage equipment.

If you want to be energy efficient then you must get a load calculation. If one is not provided then find your another HVAC contractor.

I just got 11 pages of load calcs that I am trying to decipher. I did see that for the walls, they are using "R-13.3 open cell 1/2lb spray foam insulation" and ceiling/ roof joists "R-21 spray foam, 5.5 inches in 2*6 joist cavity".

It looks like there are 3 sections, but under total building summary, I see

Total Cooling Required including Vent air 66,600 Btuh

5.55 tons based on Sensible and latent

6.92 tons based on 75% sensible capacity.

Downstairs (there is no break out between master suite which has own unit and remainder of downstairs which includes open dining room, kitchen, and living room, as well as an office and guest room which total maybe 2,700 sq ft)

Total Cooling Required including Vent air 46,900 Btuh

3.91 tons based on Sensible and latent

5.05 tons based on 75% sensible capacity.

Upstairs

Total Cooling Required including Vent air 19,650 Btuh

1.64 tons based on Sensible and latent

1.87 tons based on 75% sensible capacity.

I haven't talked to the contractor yet, but I imagine it is over sized since they have to be split 3 ways? What other values should I look for in the load calcs?

Thanks for all your help!

Neil

Design temps used both heating and cooling inside and outside.

TD

Hi TD,

I assume the you are looking for the following:

Elevation 537

Altitude Factor .981

Winter

Outdoor Dry Bulb 22

Outdoor Wet bulb 20.45

Outdoor Rel Hum N/A

Indoor Rel Hum N/A

Indoor Dry Bulb 68

Grains Diff n/a

Summer

Outdoor Dry Bulb 99

Outdoor Wet bulb 74

Outdoor Rel Hum 31%

Indoor Rel Hum 50%

Indoor Dry Bulb 75

Grains Diff 23

He has the front door oriented East when it is actually South. Does that make much of a difference?

Thanks for helping me review all of this!

The orientation makes a big difference if it means you have more or less windows facing the south. This needs to be fixed. Indoor design temperatures for summer and winter are usually 75 and 72F degrees. He has 68 degrees for the winter.

I don't understand the spray foam insulation values. Spray foam is much more expensive than traditional fiberglass batts or blown in type insulation. The primary reason for using spray foam is it have a higher R value in the same space. I would expect the wall R value to be higher that R13. The attic should have an insulation value between R30 and R40. If the master bedroom has no attic above, then I would want to build out the ceiling so that you can achieve a higher R value.

There needs to be three separate calculations for the three zones. Anything less is unacceptable.

Thanks Mike!

I will ask the builder and HVAC contractor about the R-values and why they are lower than what you state. I will also ask them to turn the house 90 degrees and provide an updated load calculation. I am sure they are going to b*tch about it, but I am paying the bills. :)

Can you please explain the temperature settings? We usually keep it a bit warm inside in summer at 74 and 70 in winter?

Thanks again!

The indoor and outdoor temperatures will affect the load calculation. The numbers I quoted are the industry standard, but they can be changed to something else. A change of one or two degrees up or down are not going to make a big difference.

So if they use 68 degrees in the winter, and you like it to be 70, then the furnace or heat pump will have to produce more heat to raise the house those 2 degrees. It should not matter unless the amount of heat the equipment produced was very close to the calculation.

For the summer if they used 75, and you like 74, then the house will need a little more cooling than calculated. Again I would not worry about it because the cooling load is increased by a lot for sensible and latent cooling.

You really want to understand what's going on with the insulation. You pay a premium for spray foam so you want your money's worth. A good strategy for a big house is to spend extra money on upgrading insulation values so that the energy bills will be lower. You want to confirm this is being done correctly. Otherwise you will have had made the extra investment will little return.

There is no excuse not to do the calculations as accurate as possible. Changing the orientation is very easy. If he complains about that then you I foresee you are going to have bigger problems later.

Thanks again. As far as the contractor complaining, I meant that he would have to go back in and redo the downstairs calculations. Hopefully he will go with it and not complaining that his work is being scrutinized.