It is just the preference of most people with Geo that I know. But if you really want to maximize efficiency and minimize operational costs, then use a programmable thermostat (which we install with all systems) and do the setbacks as you wish.

Zoning with Geo is best with a maximum of two zones per heat pump, assuming you have a water-to-air unit. The reason is that the air coil needs to have a certain minimum air flow across it and, at the same time, give up a certain amount of heat. Otherwise the compressor gets upset that you didn’t use the heat it just produced.

But again, Geo is not a fossil fuel type HVAC system. So the rules that everyone is so used to do not apply to a well designed Geo system. Geo is far more comfortable than any fossil fuel system could be, so all this zoning and setbacks is not necessary to save money.

Yes, the equations are basically what a “Manual J” calc is doing; determining the overall heat loss for your home at a given temperature.

How so? I can imagine situations where I want to vary throughout the day temperatures in different zones or through the whole house. Are there problems that will arise if I end up doing this?

About the calculations… I am just realizing. Is this a simplified version of a “manual J”? I have heard this term on another forum but just now realized what it was probably for.

Anna, we’re going to all be geo pros by the time we’re done reading your blog!

I do like the cooler temp in my house. It’s easier for me to breath, and my skin and eyes don’t dry out. If you come visit I’ll give you lots of blankets. ;-D

A gallon of oil contains approximately 138,000 Btu when burned. A typical oil furnace has an AFUE of about 84. This means that a maximum of 84% of the oil’s energy is delivered into your home for actual heating. The rest goes up the chimney.

This means that you only get 115,920 Btu (138,000 x 0.84) out of that gallon of oil. If your home needs 768,000 Btu to heat it for 24 hours at the conditions you described, it means that you would actually burn 6.63 gallons of fuel oil during that day, and this would cost you $24.45 for that same 24 hours.

64 degrees!!! Wow, I’m not coming to visit! The whole idea with Geo is that you set the temp at what you like and forget about it; no night setback, etc. They work best that way.

Rigid polyurethane foam does not have any outgassing once it cures (within 24 hours or less, depending upon the outdoor temp). The installers should be using the proper protective gear. As for the manufacturers, OSHA has strict regulations for the work environments where this is manufactured (i.e.- Dow Chemical), and I can assure you that they are adequately protected.

Besides, the mixing of Part A and B chemicals does not occur until it comes out of the spray head, so there is nothing for them to be exposed to at the plant. There is a whole discussion about all of this here on Anna’s site.

Cellulose and cotton batt insulation are not suitable for insulating under the roof sheathing. Fiberglas is acceptable, but does nothing for air infiltration. Foam is the best option.

As for calculating the heat loss, the equation is simple. You calculate the square foot area of the exterior wall surface, subtract the area of the windows and doors, and that gives you the heat loss wall area (in sq. ft.). Then you subtract the outdoor temp from the indoor temp (i.e. 64 – 20 = 44) to get the Delta T (temp differential). Next you divide the R-value into 1 (i.e. 1/21 = 0.0476) to get the U-value. Finally, multiply these 3 results together to get the total heat loss in Btu/Hr.

Repeat this same process for the area of the windows and door using their U-value (from the manufacturer) and add it to the wall loss. Do the same thing for the roof area using the R-38 converted to U-value (0.0263) and add this to your other total losses. This gives you the total heat loss per hour of the house. For 1 day, multiply this by 24 hours/day.

(NOTE: Do a Google search for an online home heat loss calculator to make this whole process a lot easier.)

A 4-ton Hydron Module heat pump on a 50ºF open loop Geo system consumes 3.4 kW (3,400 watts) to produce 50,900 Btu/Hr. Divide your total house heat loss by 50,900 and multiply it by 3.4 to get the total electricity (in kW) to deliver that heat.

If your home is 1,200 sq. ft. (1st & 2nd floor) and you heat the basement for a total of 1,800 sq. ft., then your total heat loss will be will around 32,000 Btu/Hr. insulated to the level you indicated at the temperatures you specified. For 24 hours, this totals 768,000 Btu.

The Hydron Module 4-ton heat pump would use 51.3 kW to heat the house during that day. If you pay $0.15/kWh in your area (for example), this would cost you $7.69 to heat the home. In actual operation, it would actually cost less as I used a bunch of short cuts to make this calculation and made worst case scenario assumptions.

For now, I have an additional question about insulation, now that that has come up. I’m a bit concerned about the offgassing of foam, and also the chemical exposure by workers who produce it. I’ve seen cellulose insulation and also cotton batt (blue jean) insulation. They both seem like much better alternatives from a health and environmental perspective. They do have a lower R value. Would either of these materials be usable under the roof sheathing?

Also, I am wondering if there is a formula to use to figure out how much energy a geo system will consume (in kWh) for a certain scenario. For example, if I have a 4-ton geo heater with desuperheater running in my home described above. And that home had R-21 walls and R-38 ceiling. And the day was 20 degrees outside and I kept my indoor temp at 64 degrees. Could I calculate the energy consumption (kWh) for the day?

I’ll probably have more questions once I get my energy audit results back.

If the attic is going to be unheated, then he can just insulated the 2nd floor ceiling/attic floor. He could still go with foam, or a combination of foam and fiberglas or cellulose; 2″ of foam sprayed on the 2nd floor ceiling (attic side), and then 12″ of fiberglas or cellulose over that.

The rule of thumb for DeSuperheaters is that each ton of heat pump capacity produces enough hot water for a person. So a 4-ton supplies a family of four. The Rochester house has two adults and two teenagers. But the change from 4-ton to 5-ton was strictly for the planned addition to the home.

Typically Hydron Module is the highest priced heat pump line, but it is the best equipment. It is considered the “Rolls Royce” of the industry, whereas Water Furnace (and Climatemaster) are considered to the the “Cadillac”. Hydron Module is specified by engineers more than most other systems due to its reputation for incredible quality and performance.

Did you client have to buy a bigger unit to be able to supply hot water through the DeSuperheater or are there only 2 of them?

Are Hydron units more expensive than WaterFurnance units?

Stephen, did Gary answer all your questions.

Oh, and thanks for the compliment. Gary, your advice has been invaluable on this article. (Just, the “engineer”…pleeease!)