SIP Homes

Andy_20 · February 2007

> I'm trying to get a properly sized central air 
> conditioner install in my SIP paneled home. I'm 
> doing radiant heat and don't need a furnace. I 
> want the central air to provide cooling in the 
> summer and some air exchange when needed since 
> SIPs are really air tight. Here in Los Alamos, NM 
> it rarely gets above 90 F but while in the high 
> 80s it is to uncomfortable not to have an AC. So 
> I don't need a large system to begin with, but I 
> set the outside temperature to 95 F on the code. 
> SIP aren't very common around here and I haven't 
> found an HVAC contractor familiar with them. 
> Right now I have one giving me bid and due to 
> ducting restraints between floors we thought it 
> would be a good idea to split the floors into to 
> different zones. I told him it was a SIP house 
> and very air tight and well insulated. He said OK 
> and left. I had the feeling he wasn't going to do 
> a heat gain/loss calc so I found some HVAC 
> software online that will do residential for $45 
> and had some good reviews. 
> http://www.hvaccomputer.com I did a heat 
> gain/loss on my home and came up with the 
> following figures. First Floor 1250 
> sqft Sensible Heat Gain: 7,772 BTUH Latent 
> Heat Gain: 984 BTUH Total: 8,756 BTUH Second 
> Floor 1550 sqft Sensible Heat Gain: 7,443 BTUH 
> Latent Heat Gain: 501 BTUH Total: 7,944 BTUH 
> Total House Heat Gain: 16,700 BTUH 
> 
> Which is 
> about 1.5 Tons. So I called up the HVAC 
> contractor and told him about 1 Ton per floor 
> should be fine. He baulked at the number and said 
> it is hard to even find 1 Ton units. We then had 
> a conversation and basically he only uses sq-ft 
> and CFM. He said you need 1 CFM per sq-ft and 1 
> Ton = 400 CFM. So I need a 4 Ton unit and a 3 Ton 
> unit and maybe I could get away with a 3.5 and 
> 2.5 Ton units. He said the blowers are matched 
> with the condensers so he can't get a 1 Ton 
> condenser with a 4 Ton blower. He said if he 
> found a 1 Ton unit and installed it we would 
> barely feel the air comming out and it wouldn't 
> work. I called Trane a AC manufacturer and he 
> confirmed that it will be very hard to size it 
> properly because we are both right. I need 
> something with only a 2 Ton BTUH removal and a 7 
> Ton blower but you can't do that because it will 
> ruin the equipment. Does anyone have some 
> thoughts on this. How do I get the CFM up but 
> keep the BTUH heat removal down. Or is their a 
> better cooling solution out there? 
> 
> Mark 
 
Go to www.mrslim.com. You will find exactly what you need and it will be whisper quiet. Hope this helps. Andy

Mark_92 · January 2007

Sizing SIP Homes

I'm trying to get a properly sized central air conditioner install in my SIP paneled home. I'm doing radiant heat and don't need a furnace. I want the central air to provide cooling in the summer and some air exchange when needed since SIPs are really air tight. Here in Los Alamos, NM it rarely gets above 90 F but while in the high 80s it is to uncomfortable not to have an AC. So I don't need a large system to begin with, but I set the outside temperature to 95 F on the code. SIP aren't very common around here and I haven't found an HVAC contractor familiar with them. Right now I have one giving me bid and due to ducting restraints between floors we thought it would be a good idea to split the floors into to different zones. I told him it was a SIP house and very air tight and well insulated. He said OK and left. I had the feeling he wasn't going to do a heat gain/loss calc so I found some HVAC software online that will do residential for $45 and had some good reviews. http://www.hvaccomputer.com I did a heat gain/loss on my home and came up with the following figures.
First Floor 1250 sqft
Sensible Heat Gain: 7,772 BTUH
Latent Heat Gain: 984 BTUH
Total: 8,756 BTUH
Second Floor 1550 sqft
Sensible Heat Gain: 7,443 BTUH
Latent Heat Gain: 501 BTUH
Total: 7,944 BTUH
Total House Heat Gain: 16,700 BTUH

Which is about 1.5 Tons. So I called up the HVAC contractor and told him about 1 Ton per floor should be fine. He baulked at the number and said it is hard to even find 1 Ton units. We then had a conversation and basically he only uses sq-ft and CFM. He said you need 1 CFM per sq-ft and 1 Ton = 400 CFM. So I need a 4 Ton unit and a 3 Ton unit and maybe I could get away with a 3.5 and 2.5 Ton units. He said the blowers are matched with the condensers so he can't get a 1 Ton condenser with a 4 Ton blower. He said if he found a 1 Ton unit and installed it we would barely feel the air comming out and it wouldn't work. I called Trane a AC manufacturer and he confirmed that it will be very hard to size it properly because we are both right. I need something with only a 2 Ton BTUH removal and a 7 Ton blower but you can't do that because it will ruin the equipment. Does anyone have some thoughts on this. How do I get the CFM up but keep the BTUH heat removal down. Or is their a better cooling solution out there?

Mark

Andy_20 · January 2007

Go to www.mrslim.com. You will find exactly what you need and it will be whisper quiet. Hope this helps. Andy

don_156 · January 2007

Great a sip home.

Let see fresh air issue,humidity issue..and trying to address it all with a cooling system that will properly see
very short run times.

Match the system as close to load as possible.Add a dehumidifier that you can pipe fresh air into that comes with a good filtration system and is indepently control...
And enjoy.

Mark_92 · January 2007

Ductless Split AC

I like the Mr Slim idea. I wasn't familiar with ductless split AC and after doing a little research I think it will be a cost effect method for me. I can zone a few rooms with it and put in a seperate fresh air intake system.

Eugene Silberstein 3 · February 2007

Rules of Thumb

Rules of thumb are, well, rules of thumb. Using the one cfm per square foot rule has gone the way of the dinosaur. These calculations do not take into account any of the structual characteristics of the home. These include insulation, orientation, fenestration, etc. I guarantee that his numbers are WAY TOO HIGH.

As suggested by others, check out the Mr. Slim website.

Keep us posted,

The Professor

SIP Homes

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