Help me understand this Manual J/D/S

josephny

I just received the attached heat load calculation on a house I'm in the middle of renovating. Still haven't settled on an HVAC solution, so I had this calculation done (after I did one on my own and a contractor did one).

I'd very much appreciate feedback on how to interpret this, what might stand out about, what it might indicate would be a good HVAC solution, etc.

Thank you!

Ironman

The load calc is just one tool in determining how to heat and cool a house. Other things would include the age and type of construction, occupancy use (single family, multi), the type of fuel sources available and their costs, the customer's budget vs their expected level of comfort, is this a short or long term investment?

josephny

Ironman said:

The load calc is just one tool in determining how to heat and cool a house. Other things would include the age and type of construction, occupancy use (single family, multi), the type of fuel sources available and their costs, the customer's budget vs their expected level of comfort, is this a short or long term investment?

Well, it's a gut reno of a 100 year old house which will be very well insulated (r25 walls; r49 roof; basement up to rafters in conditioned space), zone 6, electric ($0.105/kwh) and LP ($1.79/gallon) available; single family but often extended guests; long term hold/use.

Ironman

Hydronic heat is by far the most comfortable and easiest to zone, but a Mercedes comes with a much larger price tag than a Yugo.

You've done very well to get the heat loss down to 19 btus per square foot in a 100 year old house. Radiant floors in part or all of the house may be an option.

I would really have to see the house and have a personal discussion with you to determine the best option(s).

josephny

Here's some pics:

josephny

Ironman said:

Hydronic heat is by far the most comfortable and easiest to zone, but a Mercedes comes with a much larger price tag than a Yugo.

You've done very well to get the heat loss down to 19 btus per square foot in a 100 year old house. Radiant floors in part or all of the house may be an option.

I would really have to see the house and have a personal discussion with you to determine the best option(s).

Thank you again.

I would love to go with hydronic floor heat, but then I'd need another system for AC and for ventilation -- and that would (I think) be way over budget.

It's looking like either ductless or ducted minisplit heat pumps.

pecmsg

My ideal system is radiant to take that chill off the floor with HW coils on the A/C ducts. 

josephny

pecmsg said:

My ideal system is radiant to take that chill off the floor with HW coils on the A/C ducts. 

From what I've learned (thanks in great part to you), that is a fantastic solution. I think it's also substantially more expensive than a ductless or ducted split system.

josephny

I keep studying this heat load analysis and getting more and more confused.

Besides the fact that I can't reconcile how the system gets 7291 btu/h from 3160 sq-ft of wall space, 11970 btu/h for 1460 sq-ft of roof, and 33986 btu/h from 850 sq-ft of window, why does it add 26278 btu/h for the ventilation heat load (364 CFM) when I plan to use a Fantech 260D ERV?

Is the ERV supposed to lower the heat load, or only lower it compared to opening a window and getting the same ACH using the open window method?

All the basic/simple online man-j calcs I use give me something between 30k-40k total heat load, whereas this gives me 76k (including the ventilation load).

Other than to satisfy my serious curiosity, this work is so that I can come up with the the right designed and sized HVAC system.

This house is in zone 6 at 1200' AGL.

Thank you!

pecmsg

josephny said:

pecmsg said:

My ideal system is radiant to take that chill off the floor with HW coils on the A/C ducts. 

From what I've learned (thanks in great part to you), that is a fantastic solution. I think it's also substantially more expensive than a ductless or ducted split system.

You get what you pay for.
Your mini splits are not good for recovery from set backs, need defrost from time to time.
Ducted systems in unconditioned spaces allow warm air to move into the ducts, Cool and condense any moisture in the air back to water. Then slowly drift out of a vent. Happens quite a bit in the NE with attic installations. Solution a HW coil.

josephny

pecmsg said:

josephny said:

pecmsg said:

My ideal system is radiant to take that chill off the floor with HW coils on the A/C ducts. 

From what I've learned (thanks in great part to you), that is a fantastic solution. I think it's also substantially more expensive than a ductless or ducted split system.

You get what you pay for.
Your mini splits are not good for recovery from set backs, need defrost from time to time.
Ducted systems in unconditioned spaces allow warm air to move into the ducts, Cool and condense any moisture in the air back to water. Then slowly drift out of a vent. Happens quite a bit in the NE with attic installations. Solution a HW coil.

By "recovery" do you mean money or energy?

My plan is to not have any unconditioned space. From basement through 3rd floor whose ceiling is insulated and right below roof, all will be conditioned.

And HW coil means air handlers with vents and HW coils, right?

This can be done with heat pumps or best with propane boiler?

And what about AC?

Thanks!

Jamie Hall

First, on the energy recovery ventilator. They will recover some -- but not all -- of the heat in the exchanged air. Thus, in comparison with an open window, they will save energy. However, they do nothing for the heat loss through the structure. From the numbers you have provided, I believe that the structure heat loss is around 54,000 BTUh; adding 20 K or so to that for the ventilation seems quite reasonable.

Now on the heat source. As others have suggested, with that low a heating load you should at least consider hydronic radiant heat in the floors, since you have the structure open. That would supply your base heating load and is very comfortable. You could then -- and I would -- supplement that with hot water baseboards or panel radiators, to provide the rest of the heat and to provide you with a way to easily raise or lower the temperature of spaces as needed (within reason, of course -- more than a few degrees up or down is not going to work well).

You could use minisplits or a ducted system for the air conditioning and, if you go for heat pumps instead of air conditioning only, for heat in the shoulder seasons. They are not as satisfactory as a properly designed and installed ducted system, but they are less expensive and there are not ducts to run. Neither they nor a ducted heat pump system will be satisfactory in colder weather.