1st foam house - seem to be undersized ?

[Timber]

Just started up 3 ton Rheem on open cell foam new construction. Foam on outside walls and roof rafters. Was 96 in house yesterday when I started unit, ran all night, checked at 7 am this morning, only pulled down to 83 inside.

This is giving me a bad feeling in my stomach if you know what I mean.

House is 2600 sq. ft. It also has been extremely hot here. 106 and 107 day after day. The design temp for this area is 97.

Question , how should I handle the ceiling load calc when the insulation is up on the roof rafters. Now the whole attic space is being cooled .
I may be ripping this system out and going larger.

[MM#7]

Just started up 3 ton Rheem on open cell foam new construction. Foam on outside walls and roof rafters. Was 96 in house yesterday when I started unit, ran all night, checked at 7 am this morning, only pulled down to 83 inside.

This is giving me a bad feeling in my stomach if you know what I mean.

House is 2600 sq. ft. It also has been extremely hot here. 106 and 107 day after day. The design temp for this area is 97.

Question , how should I handle the ceiling load calc when the insulation is up on the roof rafters. Now the whole attic space is being cooled .
I may be ripping this system out and going larger.

tell the customer all the humidity you're taking out of the air!

[air2spare]

You could install return ducts into the living space ceiling, add insulation so you dont have the attic load to the house.
Do you have a heatload calculation?

[Timber]

You could install return ducts into the living space ceiling, add insulation so you dont have the attic load to the house.
Do you have a heatload calculation?

I used wrightsoft. But maybe my data entered was off for the ceiling load.

I was thinking about insulation above the ceiling to remove or lessen the ceiling load.

Just talked with another local contractor a they are sizing the units the same regardless of the type of insulation used. That being said this would have been a 4 ton unit.

Air2spare when u say add returns in ceiling, you would also tie them into the return plenum at unit. Right.

[EugeneTheJeep]

Done a few foam houses, I always size the same as non foam as well.

[Timber]

Done a few foam houses, I always size the same as non foam as well.

Well I think I screwed up. Makes me want to say some cuss words .....

[MM#7]

Well I think I screwed up. Makes me want to say some cuss words .....

hey timber, wow, where i come from, we call that a money loser!!!
i feel for you. these days i don't do any new installs, i do repair,replacement,service, no money$ in installations, any way good luck, really, been there done that! again good luck!

[teddy bear]

You have a few things to check before going off the deep end. The refrigerant change and air flow over the cooling coil are the starters. Over charge or undercharge will reduce btus moved. The coil temp should be 25^F below the return air temp. Lower coil temp improves latent removal and but slows sensible cooling. In your case, to improve the sensible cooling, you could start with -20^F coil temp.
What is the situation on fresh air ventilation? Limit the fresh air to 70 cfm when occupied.
Also, are all of the blinds and window covers inplace? Solar gain is a killer that can be slowed with shade, blinds, or other ways.
More info on the temp/%RH, coil temp, and superheat/subcool. Is the outside condenser clear of obstructions and free air flow.
Regards TB

[Timber]

You have a few things to check before going off the deep end. The refrigerant change and air flow over the cooling coil are the starters. Over charge or undercharge will reduce btus moved. The coil temp should be 25^F below the return air temp. Lower coil temp improves latent removal and but slows sensible cooling. In your case, to improve the sensible cooling, you could start with -20^F coil temp.
What is the situation on fresh air ventilation? Limit the fresh air to 70 cfm when occupied.
Also, are all of the blinds and window covers inplace? Solar gain is a killer that can be slowed with shade, blinds, or other ways.
More info on the temp/%RH, coil temp, and superheat/subcool. Is the outside condenser clear of obstructions and free air flow.
Regards TB

I will check the charge this afternoon. This unit is coupled with 90 % furnace running on Hi for cooling. Probably not going to get anymore Sensible out of that.
ERV is not hooked up yet.

[MM#7]

I will check the charge this afternoon. This unit is coupled with 90 % furnace running on Hi for cooling. Probably not going to get anymore Sensible out of that.
ERV is not hooked up yet.

hey timber, what's the delta over the coil? got enough return coming back to the furnace? you pprobably ck'd already, but trying to give you moral support!

[BaldLoonie]

Around here, a 2600 sq ft house would usually have a 3 ton even with R11 walls and some blown in the attic. We just came off a stretch of upper 90s and very high humidity and people did just fine.

I'm with the rest, give the place a chance to cool down & dry off and see how it does.

I remember my foaming buddy telling me of a job where the HVAC sub oversized the equipment since he didn't believe the size the calc called for. HO had lots of humidity issues.

[Timber]

Around here, a 2600 sq ft house would usually have a 3 ton even with R11 walls and some blown in the attic. We just came off a stretch of upper 90s and very high humidity and people did just fine.

I'm with the rest, give the place a chance to cool down & dry off and see how it does.

I remember my foaming buddy telling me of a job where the HVAC sub oversized the equipment since he didn't believe the size the calc called for. HO had lots of humidity issues.

Sounds good, our summer here has broken all the records, wish these 100+ days would break. We have had like 45 days over 100 so far. a couple of weeks ago it hit 110. Its like Arizona but in the pineywoods of East Texas.

[teddy bear]

Another thought. Make sure you do not have a kink in the suction line going back to the compressor. Also extra long suction line without upsizing. Both really kill capacity.
Good luck
Regards TB

[air2spare]

Well I think I screwed up. Makes me want to say some cuss words .....

If you want to call me I will discuss a few ideas about it

[air2spare]

Well I think I screwed up. Makes me want to say some cuss words .....

If you want to call me I will discuss a few ideas about it

[MM#7]

If you want to call me I will discuss a few ideas about it

hey timber, it can't hurt to call this person, sometimes two heads are better than one, good luck!

[meh70087]

When we first started doing foam houses we didn't trust the load calc but stuck with it and have not had the first problem. Approx 3200sqft with a cool 2.5 tons. At start up I was kinda feeling like we may have some issues. Told HO we would be back in two days, when I returned she had the biggest smile ! Give it some time. No one has mentioned AIR FLOW so that may be something to check? This is also in south LA . ALL FOAM HOMES GET HEAT PUMPS unless HO refuses.

[tipsrfine]

Hey Timber, is the air handler & ductwork in the attic? My understanding about foamed attics at the roof is that there is an increase to the cooling load compared to traditionally insulated attics at the ceiling, but if the ductwork is in the attic, then there is a net reduction to the cooling load due to having brought the ductwork into the conditioned area.

[gevans]

106 and 107, day after day?
I'd give it another day before I decided anything was wrong. You have to pull out all the humidity and cool down the structure before it will run "normally".
Let us know how it's doing tomorrow.

[air2spare]

Use heat rise method to determine enough cfm delivery.
measure delta across the coil and measure coil capacity.
measure static pressure