Equipment Sizing for Geothermal

[batman71]

I recently solicited proposals for a geothermal system for my new home. I provided the house plans and other needed information so that both installers could run J calcualtions. There is nothing unique about the home design...ranch with a walk-out lower level, 3 bedrooms and about 3,200 sq.ft Both companies are well established, reputable players in the local HVAC marketplace. One quoted a 3 ton Waterfurnace system and the other a 5 ton Carrier system.

With the sophisticated tools available today and considering how long contractors have been doing these calculations, for the life of me I can't understand how the results can vary so much. I hate to think that I should be hiring a consultant to give me an unbiased and (hopefully) accurate analysis for what would seem to be a simple project.

Any tips on how to evaluate which installer's sizing I should trust, if either one?

[BaldLoonie]

Tell them what the other said and see what the response is. I usually think the lower bid is more accurate. Dealers aren't going to take a chance and undersize. They usually oversize since you won't know the difference unless you have humidity issues. New contruction you ought to put some money into a tight home, maybe some foam insulation, etc. Will save on the juice bill for decades to come.

[batman71]

Point well taken. On the other hand, could it be that the installer proposing the 3 ton unit is doing so to get his quoted price down?

Construction will be 2x6 walls with dense pack cellulose (Nuwool).

[dan sw fl]

I recently solicited proposals for a geothermal system for my new home. I provided the house plans and other needed information so that both installers could run J calcualtions. There is nothing unique about the home design...ranch with a walk-out lower level, 3 bedrooms and about 3,200 sq.ft

hiring a consultant to give me an unbiased and (hopefully) accurate analysis for what would seem to be a simple project.

What is the heating load?
++++++ Cooling Load?

Walk-out lower level is somewhat unique. One certainly does not see them Everyday.

Is the 3,200 square feet .. 1,600 sq feet on each level?
How much of the lower level is exposed to the outside air?
What is the r-value of the wall (provide type of wall and insulation) that is exposed to the outside air?

Is the ceiling insulation foam or blown in / amount?

How much windows surface area faces in each direction? U and SHGC values?

Location ? Mexico - U.S. - Canada or Europe?
Load depends on the state and city.
i.e. Northern CA and Southern CA are more than 500 miles apart and entirely different climates.

OR
just send me PDFs of house plans and BOM. Address in my profile.

- THAT SIMPLE _ Project only takes about 2 to 4 hours as a Block (whole house) Load on a 2 story residence. Maybe 10 or 20 hours for the room-by-room design. One should have this completed about 3 months prior to start of construction.

[dan sw fl]

Point well taken. On the other hand, could it be that the installer proposing the 3 ton unit is doing so to get his quoted price down?

Construction will be 2x6 walls with dense pack cellulose (Nuwool).

http://www.nuwool.com/Products/Cellu...gySavings.aspx

What is the quoted savings from NuWool?

[beenthere]

1 may be sizing to the cooling load, while the other is sizing to the heating load.

[motoguy128]

Location makes a big difference. Sometimes you need to size Geothermal for heating and either sacrifice humidity control in summer, or look into a while house dehumidifier.

Ideally geothermal targeted water source heat pumps would recognize this issue and integrate hot as reheat coils in their units for humidity control and even start offering larger standard units like 6 and 7.5 tons for the residential market.

Pretty common for a geothermal home to be a big cool & clammy in the summer due to poor humidity control.

[motoguy128]

http://www.nuwool.com/Products/Cellu...gySavings.aspx

What is the quoted savings from NuWool?

My own personal opinoin, I hate cellulose. To many potential issues with moisture. Being dense pack, it might not settle so much, but it will settle some eventually. I don't like fiberglass because it's R value drops off fast if the structure isn't air tight. Foam or even ICF walls structures are the way to go. Just my biased opinion.

[skippedover]

We've done a lot of geo systems and always size for heating at 98% factor. That is, the coldest weather 98% of the time. The bottom 2% is short term and can be handled with aux heating. That said, we always install either multiple 1-stage systems or 2-stage units to help accommodate the difference between winter heating and summer cooling. Cooling is generally about 50% of heating in our area. Now our prayers have been answer with modulating compressors. ClimateMaster now has a modulating unit and I'm sure others do or will shortly. With modulation, you can size for heating and easily accommodate all the cooling needs with good humidity control as well. I suspect 3-tons is the cooling load and 5-tons is the heating load, as stated by beenthere. As such, I'd go with the 5-ton systems, 2-stage or modulating. If you go 3-tons with a 5-ton heating load, you'll be paying a lot more for heat with the aux electric heaters. That's generally not the preference for geo systems.

[dan sw fl]

Ideally geothermal targeted water source heat pumps would ... .. and even start offering larger standard units like 6 and 7.5 tons for the residential market.

I F a residence actually needed > 5 tons, it ALSO REQUIRES 2 Units simply due to Air Distribution / Ducting issues.

[motoguy128]

I F a residence actually needed > 5 tons, it ALSO REQUIRES 2 Units simply due to Air Distribution / Ducting issues.

In the north, a 80k BTU furnace is pretty common, that's 6.5 ton of heating if you don't want heat strips coming on. That size home won't be unusually large. We have plenty of 7.5 and 10 ton water source commercial units at my work. Why not in residential. With the increased efficiencies on the newer units, you should still be able to get up to 7.5 ton with a 230VAC single phase system. You could also do 2 or 3 stage with 2 compressors.

[SkyHeating]

Now our prayers have been answer with modulating compressors. ClimateMaster now has a modulating unit and I'm sure others do or will shortly. With modulation, you can size for heating and easily accommodate all the cooling needs with good humidity control as well.

Try and buy the tranquility 40, they are over a year away from actual ship date from everything I have heard. If you want a modulating system get a WaterFurnace 7 series the ONLY modulating geothermal system available to buy today(I bought one Friday and put it in this Thursday) and the most efficient at 41EER and up to 6COP at 50% load. If you are in Portland call me and I can quote a system being the areas only geopro dealer.

Another design consideration is BTU capacity and actual not rated EWT. Most geothermal systems are rated for at most 36,000 BTUS(assuming 3 ton) if EWT is 50+ yet actual loop temps can get into the 35 degree range providing only 29,000 BTUs, some will account for this with a larger unit and others just don't understand actual vs rated capacity.

[teddy bear]

I recently solicited proposals for a geothermal system for my new home. I provided the house plans and other needed information so that both installers could run J calcualtions. There is nothing unique about the home design...ranch with a walk-out lower level, 3 bedrooms and about 3,200 sq.ft Both companies are well established, reputable players in the local HVAC marketplace. One quoted a 3 ton Waterfurnace system and the other a 5 ton Carrier system.

With the sophisticated tools available today and considering how long contractors have been doing these calculations, for the life of me I can't understand how the results can vary so much. I hate to think that I should be hiring a consultant to give me an unbiased and (hopefully) accurate analysis for what would seem to be a simple project.

Any tips on how to evaluate which installer's sizing I should trust, if either one?

No mention of fresh air ventilation? Climate? These are critical issues. Are you concerned about humidity control through the 4 seasons?
Regards TB

[54regcab]

The cost of the increased capacity of a Geo system is that more ground loop piping is required of closed loop systems. Piping/digging costs need to be considered. Depending on your electric rates payback time may be long when compared to using AUX strip heat to cover the difference on those really cold days. On the other hand if the digging equipment is already on site the extra looping may not cost that much more.

[batman71]

Thanks to everyone for the feedback.

I got some additional details from one of the contractors and have an additional question.

Contractor "B" calculated the heating/cooling loads at 57,200/49,000 and is recommending a 5 ton Comfort-Aire system which I understand is manufactured by Climatemaster. Company "D" calculated loads of 61,600/36,100 and is recommending a 3 ton Waterfurnace system.

I am assuming that "B" is suggesting the 5 ton system to cover the heating loads. However, "D" says that their 3 ton system will cover 96% of the heating load they arrived at. Is it possible that the heating capacity of the 3 ton Waterfurnace equipment would be similar to the heating capacity of a 5 ton Comfort-Aire?

BTW, 54regcab, the geothermal will be "pump-and-dump".

[SkyHeating]

Thanks to everyone for the feedback.

I got some additional details from one of the contractors and have an additional question.

Contractor "B" calculated the heating/cooling loads at 57,200/49,000 and is recommending a 5 ton Comfort-Aire system which I understand is manufactured by Climatemaster. Company "D" calculated loads of 61,600/36,100 and is recommending a 3 ton Waterfurnace system.

I am assuming that "B" is suggesting the 5 ton system to cover the heating loads. However, "D" says that their 3 ton system will cover 96% of the heating load they arrived at. Is it possible that the heating capacity of the 3 ton Waterfurnace equipment would be similar to the heating capacity of a 5 ton Comfort-Aire?

BTW, 54regcab, the geothermal will be "pump-and-dump".

I will assume the WaterFurnace dealer is quoting a Series 5 unit which shows at a 50 degree EWT a heating capacity of 34,400 BTU's total so if your heat load is 61,600 and they are quoting a 3 ton they are basing on cooling load only(which often is industry standard) however you should be putting in two stage equipment so first stage meets your cooling load and second stage meets your heating loads. I would not put in less than a 5 ton with that heating load and would make sure its two stage or variable capacity equipment to match to cooling load.

[dan sw fl]

I will assume the WaterFurnace dealer is quoting a Series 5 unit which shows at a 50 degree EWT a heating capacity of 34,400 BTU's total so if your heat load is 61,600 and they are quoting a 3 ton they are basing on cooling load only(which often is industry standard)

However you should be putting in two stage equipment so first stage meets your cooling load and second stage meets your heating loads.

I would not put in less than a 5 ton with that heating load and would make sure its two stage or variable capacity equipment to match to cooling load.

Batman71's Manual J analysis actually shows heating and cooling loads are nearly equal.

I am not aware of the water source temperature for central OH.

[SkyHeating]

Batman71's Manual J analysis actually shows heating and cooling loads are nearly equal.

I am not aware of the water source temperature for central OH.

Both his load show over a 20% difference between heating and cooling which is over a .75 ton difference on one and a 2 ton difference on the other calculation. Part of it will depend on what water temperatures they expect on the pump and dump system, the 50EWT is what most use for ratings but it could be in the high 30's for heating or in the mid 70's and above for cooling which would once again change the capacity of the unit. There is not nearly enough information to accurately assess the situation but something does not seem right for a 3 ton system that will cover 96% of a 61,600 BTU heating load.

[batman71]

My original problem and perhaps the first priority based on what I am hearing here is that I need to get an accurate load calculation. I have figures from three contractors who have quoted the job and am no more sure of the loads than when I started.

I ran across a company that makes impressive claims about their ability to provide this analysis and have been giving some thought to using their services.

http://www.load-calculations.com/Contact_Info.html

Any opinions on this approach or any suggestions on where to turn to get "unbiased" and accurate load calcualtions?

[arc8]

Knowing what I do as a designer and installer; I would look for one that does Load-calcs consistently and selects the equipment accordingly. I would then ask for recent install systems installed by them. Matter of fact I highly recommend that you look at a Annual operating cost analysis performed by them! Knowing what I know, anything less than this is not enough to satisfy me!

Best of luck.