Geo sized too small at 70%

[cleangreen]

There aren't too many geothermal installers in my area. The one I'm dealing with is recommending the 4 ton Climatemaster, even though it can only produce 37,500 BTU at full load, which is just over 70% of my home's heatloss (52,000 BTU). That sounds small to me. Can anyone help me understand if the system is properly sized?

[beenthere]

Does it meet the heat gain?

[cleangreen]

There is a line on the report that says "Avg. internal gains: 10,800 Btu/Hr" is that what you are looking for?

[beenthere]

Whole House 2,861.7 sq.ft. sensible gain 28,150 latent gain 8,810 total gain 36,960 heatloss 42,535

Something like that.^^^^^^^

[cleangreen]

Here is the info I have from the report:

Total Heated Area (inc bsmt): 3773 sq. ft.
Total Building Heating BTU 52,925
Total Cooling BTU BTU 36,885
Sensible Cooling 28,401
Avg internal gains 10,791

Hopefully that is enough information to help you help me!

[geodude]

There aren't too many geothermal installers in my area. The one I'm dealing with is recommending the 4 ton Climatemaster, even though it can only produce 37,500 BTU at full load, which is just over 70% of my home's heatloss (52,000 BTU). That sounds small to me. Can anyone help me understand if the system is properly sized?

what was your indoor design temp and outdoor winter design temp ( wetbulb)

[cleangreen]

I'm not sure what a wet bulb is, but here are the design temps listed by the GeoDesigner program report I received.

Winter design -2 deg F
Summer design 84 deg F
bld balance 57 deg F

Winter Indoor 72 deg F
Summer Indoor 75 deg F

Delta T: 74 winter / 11 summer
Summer daily range 22 deg F

Hopefully the wetbulb is in that information.

[Buck_Taylor]

Here is the info I have from the report:

Total Heated Area (inc bsmt): 3773 sq. ft.
Total Building Heating BTU 52,925
Total Cooling BTU BTU 36,885
Sensible Cooling 28,401
Avg internal gains 10,791

Hopefully that is enough information to help you help me!

Where is the project located?

My initial response for a heating dominated climate would be no, the unit is too small for your heat loss. The issue with Heat Pump sizing in conventionally built homes is you either size it for heating and it will be too big for cooling, or you size it for cooling and it will be to small for heating.

In your situation the unit is appears to be a comprimise between the two. You will need to have supplemental heat (2nd or 3rd stage) to make up the difference during the colder weather. Again, if you live in a heating dominated climate, you want this part of the system operation to be efficient, otherwise it will cost too much and you loose the efficiency benefit of the heat pump. If you have gas hot water, you could add a hot water coil in the ducts to do this relatively affordably.

If you choose to upsize your heat pump, you will need to have larger ducts, so this may be a limiting factor too (as to how big a unit you can connect to any existing ducts). Duct sizing is extremely important in getting heat pumps to operate correctly, so simply picking a larger heat pump may not actually get you any additional BTU's (plus it will be less efficient)!

If you are in a cooling dominant region, then this system is fine, The amount of back-up resistance you use will be very affordable and there is no reason to complicate the design.

PS - Ignore the average internal heat gains. That is not part of proper sizing routines for heating. It can be used for cooling, but is already accounted for in the peak calculations. That is something use to calculate energy consumption. We asked WaterFurnace to remove this fromtheir spreadsheet calculator 10 years ago when their dealers were running into problems here in the NE. WaterFurnace dropped the whoel spreadsheet and then ClimateMaster picked it up and used it in a stand-alone application they had developed. The proper way to determine loads is to use ACCA Manual J methods. It is independent of the sales spin any manufacturers wants to give. Once teh load is calculated, then you can decide what the proper piece of equipment is to satisfy the load conditions.

[beenthere]

That will give you a balance point of about 17*F.
So around 19*F you would want your aux to come on with that match up.

As above its been sized to the cooling load, plus 25%.
Common for air to air heat pumps. (I realize your going geo)

[cleangreen]

Thanks everyone. I'm in Brampton, Ontario so we are certainly a heated dominated climate.

Do you mean that at 19 defrees fahrenheit I would need to use the electric heat back up? That's only -7 degrees celsius, which is a good part of my winter.

[beenthere]

If your load calcs, and performace ratings are acturate.
Yes, the HP would need the aux to come on with the HP to maintain stat set point at any temp under 17*F.

Its common to bring the aux on 2*F before they are really needed to prevent eternal HP run time, and lose temp because of high winds.atleast on air to air systems)

In Canada, they have their own load calc system which is rumored to be a bit more acturate then Manual J. Ask you contractor to use it, and see if it changes the load calc lower or higher.
The more acturate the calc, the better equipment can be selected for the application.

[wagnerhvac]

Is Guelph near you?

I put that in geodesigner with your info

Your balance point would be 13 degrees
first stage heating 69%

first stage cooling 100%

aux heat require 5 KW

full emergency 16 KW

The geo will do about 96% of your heating with 4% back up

This all figuring verticle bore with 1 inch pipe

[heatpumpguru]

You guys make me PROUD!!

[Carnak]

can see them installed for 70 to 80 percent in some extreme climates. Could work out to 90 to 95% of the heat you need each heating season comes from the ground 5 to 10% the auxiliary heat working on top of the geo unit

where i used to live you could size them to meet the entire heating load but it was like diminishing returns. Those sized for the full load were way oversized for cooling.

Where I used to live was not very humid in the summer so never had a high humidity problem from the over siizing. May be different in your neck of the woods


You need to talk to someone who knows the 'bin weather data' for your area

[cleangreen]

Wow, these are all good comments and I will speak to my contractor about them. Thanks for all of your help - my contractor may not like you in the morning, but you guys are doing a great service for us simple folk!!

Guelph is not too far away, and would have slightly colder temps in the winter. I'm still not sure I'm comfortable having to use the auxillary heat at only 13 degrees. My contractor had said 99% of heating will be done with geo and 1% auxillary. I'm still not sure how that can be when the btu output is only 70% of the homes heatloss, but I think 1-4% auxilary heat in Canada is too high for a system of this cost (vertical drilling would be required).

[Carnak]

I based my commets on NW Ontario, was not uncommon to see 70 to 80 percent sizing up there

Back then I would say with electric heat, your were a dollar a square foot for the heating season, that was 8 cents a kWh, and in a colder place then Guelph.

Heat pump with the auxiliary maybe cut that down to say by a factor of 2.5

[beenthere]

Don't forget. The heat pump will be running even when the aux is heat is on.
When its 10* outside, the HP will be providing the majority of your heat, not the aux.

If your heat pump is providing 70 percent of the heat you need at -2, the aux is only providing 30%.

So, less then 5KW of aux at design temp.

[Carnak]

ask him how much more to go to the next size larger and drilling another hole. Also price a dehumidiefier.

Maybe going the next step up knocks off $75 dollars of the yearly heating cost compared to the one sized for 70%

[fsq4cw]

A geothermal system designed to provide 70% of your peak load (the coldest days) is properly sized, as such a system will provide 95% of the heat requirement of your heating season, will also be properly sized for cooling and provide the greatest economy of operating and installation cost resulting in the fastest payback.

As correctly pointed out in another post, the backup runs in addition to the HP - not instead of the HP. For about 5% of the winter don’t get hung up on the backup – that’s how it’s supposed to be designed and operated!

SR

[tbox8098]

One way we do it in Minnesota to get the maximum efficiency is to use 2 stage equipment. This way you are able to size for 95-100% of the heating load and almost never having ot use and supplemental. You also do nto sacrifice your dehumidification during the summer for the a/c

Just my 2 cents

Tj