1st foam house - seem to be undersized ?

[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

[Timber]

correction ...2200 sq. ft.

[rickboggs]

I may be ripping this system out and going larger.

Don't do it.

Make sure the equipment is running at full capacity, a good way to do that is to use udarrell's Enthalpy Chart. Then wait until the weather is within design parameters. It's not realistic to expect a piece of equipment to work as designed when design conditions are out of whack by 10 degrees.

[MechAcc]

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.

Yes but have you measured the TESP and plotted the air flow on the blower chart to determine that airflow is 1200 cfm for the 3 tons not 2000 cfm?

[arc8]

I once ran into something like this but it was the other way; a furnace.

I sized up this new small house. The heat loss was 32,000 @ -24 degree, so I installed a 92% 40,000 furnace.

The installation happened in the middle of winter, we got the furnace going, the drywallers were mudding. It was insulated everywhere except the basement which were poured concrete walls.

Needless to say, the furnace could not keep up, it would not warm the house above 65 degrees on average cold days for a few weeks. I hoped that I calculated the Heat Load correctly. I was a little nervous. But after a month, it corrected itself. The house was completed and the folks moved in and to this day it is able to heat the house above 75 degrees on the coldest days.

I guess the Heat Loads were meant for finished and stable (constant) temps on the inside.

Good Luck to your project.

[kjkircher]

Make Sure the Ridge Vent on roof has been properly installed and make sure thermostat on attic blower is properly set. Ditto on separating the attic load via proper placement of returns(insulate them well)

AND make sure Walls are properly stopped at the floor and ceiling plates. If they are not, each wall space will function as a heated chimney spilling air into the living areas via flooring systems.

[frumper15]

This is something that I have found as well - our first Geothermal install also happened to be a foam insulation job (house fire rebuild). Of course, the homeowner didn't tell me that during the design phase, and the plans didn't specify so my load calcs and equipment sizing were based on conventional insulation, etc. Well, they sprayed the underside of the roof (cathedralized?) and made the attic a conditioned space so the interior volume went up by another 25% or so. I was a little nervous at startup because 1) it was my first Geothermal and I was trusting my training and calculations and 2) I had sized a 4 ton geothermal where we probably would have installed an 80k BTU furnace. When the system first started up it was middle December and below freezing outside. Thankfully, the HO had been keeping things warmish with a kerosene torpedo heater so I wasn't trying to come up from too low, but without resorting to the auxiliary heat it took a while to chip away at those degrees.

The lesson I learned is that an appropriate sized system will do a great job of keeping the space at temperature, but extreme recovery is another story. New startup in the middle of record high temperatures? A few days at the very least before getting worried.

We had a similar issue with our service side last month - record highs for a few weeks and lots of broken down systems. The house would be 90 degrees inside when we got the system running again and the customers would be calling 2 hours later complaining that it wasn't 70 degrees in the house yet. I told all of them to call back 24 hours later if it wasn't the temperature they wanted - I didn't get any calls.