Figuring heatloss on a super tight home

kcopp

Running into a head scratcher on a newer home.
Customer has 2 air source heat pumps and is not a huge fan. Just does not keep him warm.

Wants a hydronic system.
Figuring on a wall hung mod con w/ panel rads.

The heatloss number do not compute. There seems to be no good way to make adjustments to the home being super tight. No diferentiation if the air infiltration is 10 changes per hour or 1 air change per hour.

House has a HERS rating of 52 and had a blower door test less than 1 change per hour.
R51 in ceiling,26 in walls. ICF foundation and slab

Is there a program that allows for this?

Zman

Siggy's software let's you set the ACH to whatever you want.
You can download a trial version for free.
https://www.hydronicpros.com/downloads/

Larry Weingarten

Hello, Could you calculate the heat contribution from the heat pumps and then add electric space heaters and measure that energy consumption over a month? This way, you could calculate the energy needed to keep the house warm from actual use. Maybe?

Yours, Larry

pecmsg

Small HW Coil on each supply duct?

What do they have for bringing in outside air?

pecmsg

http://www.fantech.net/product-range/fresh-air-appliances/

Jamie Hall

Is a heat exchanger being used to bring in fresh air and exhaust stale air? I certainly hope so... but if so, you are going to need data on the efficiency of that unit. Just to add to the confusion...

kcopp

He just wants to use a new system to heat the home.
The Ductless mini split will still be there.
The Air Exchange will still be there.

Rich_49

kcopp said:

Running into a head scratcher on a newer home.
Customer has 2 air source heat pumps and is not a huge fan. Just does not keep him warm.

Wants a hydronic system.
Figuring on a wall hung mod con w/ panel rads.

The heatloss number do not compute. There seems to be no good way to make adjustments to the home being super tight. No diferentiation if the air infiltration is 10 changes per hour or 1 air change per hour.

House has a HERS rating of 52 and had a blower door test less than 1 change per hour.
R51 in ceiling,26 in walls. ICF foundation and slab

Is there a program that allows for this?

Was this > 1 ach the ACH nat or ACH50 ?

kcopp

50 pascals
Nat 0.03
Ach @ 50... 0.08

CFM @ 50... 465

Jamie Hall

The key to it is going to be that air exchange -- which I hope he keeps running. The apparent heat loss you can figure -- use the lowest air change that Siggy's program will allow, and go with that. Then... figure the heat needed to warm the incoming air from the air exchanger up to the desired temperature in the building (worst case for that arithmetic is to find the volume and the delta T needed, and the heat capacity of air, and do some multiplying). Add that to the heat loss from Siggy's program.

I'd consider putting some of that required heat into coils in the intake duct from the exchanger, to eliminate cold draughts, and then the rest of it into the panel rads...

Solid_Fuel_Man

I live in a home with similar construction. I've found heat loss to be much more of a flat line than the steep lines we are used to. Think of doubling a small number, it's still a very small number even though it's 200%.

I burn pretty much the same amount of wood when it's 20 degrees outside as when it's 0 outside. R32 walls a d R60 ceilings. 1ACH were my calculation. 14btu/ft2 at -40F.

As @Jamie Hall said, the air exchanger may be the largest heat loss from the home.

What @Larry Weingarten said, only is use 100% electric heat for a month to calculate real world heatloss, mini splits can vary their output so much based on outdoor temp and outdoor humidity necessitating many defrost cycles. Hard to put a real world number on what their actual output is for a given period of time. Electric heat is easy, 100% efficiency all day long. Add some Kill-A-Watt meters and a portable heater for each area and you have some real numbers.

kcopp

Thanks guys.
You would think it would be straightforward.
A lot of guys talk about " fluff " in the manual J calculations.
Getting high numbers in this place that is supposed to be energy star rated.
I tried the Hydronic Pros version and had a hard time figuring it out in the 15 min window they give you.
Ill keep plugging away.

delta T

Get siggy's software, it is amazing. Does a lot more than heat loss, and you can really go down the rabbit hole tweaking the heat loss number using different ACH, different construction.

Mark Eatherton

Roll your own using a spreadsheet. A/R * delta T, or U * A* DT. A = area, R = R value, DT = differential in temperature, U = U value (inverse of R value). You have to use all common denominators, and windows are the only thing I've seen that come with a U value instead of an R value. U is the inverse of R, and vice versa.

Figure can't lie. If you really want to fine tune it, then calculate the R value of all wooden framing components, and calculate them separately from the stud bay cavities.Wood has an R value of roughly 1 per inch, so a 2 X 6 stud wold have an R value of 5.5 . You have to calculate the total square footage the studs displace, and don't forget to deduct that amount from the wall as a whole.

Infiltration is calculated as volume * .018 * DT * Air Changes per Hour (ACH). You know what that number is, so no guessing needed there.

ME

jumper

In super insulated tight homes heat load can depend on how often door is opened? So you have to oversize. Sounds like it's a matter of customer's comfort. Does she need the energy savings from heat pump if house is Canada 2000 standard? I'd look at ceiling hight electric radiant heaters because then there is individual room control and people feel warmer. Except maybe when they sit at table or desk.