I'm building an off grid house and have had 3 companies bid HVAC systems. So far we have bids for 5 standard HVAC systems and they are 1.5 ton and 3 bids for mini split systems but the numbers don't match very well between the bids.

I've been doing a lot of reading on geothermal and looks like it might be the way to go. From looking at installation guides most call for a min 31 to 40 OCP but it looks like it's for the product line not the smaller unites.

I did contact 2 of the better know companies by email and got lots of great information but are not giving me any answers.

I'm more concerned about running amps and not the starting amps.

I don't think you will find anything will beat geo on a btu per kwh basis. Maybe diesel or propane for micro CHP heating. Amps you can approximate from COP and btu output.

Do geothermal units use large compressors like standard HVAC units?

I would expect that a 2 ton geo system will have a compressor about the size of a 1.5 ton mini-split. There is no free lunch that allows any unit to use less amps for a given output and COP. OK, minor things like power factor and outdoor compressors.

Copeland scroll (R410) RLA is about 10amps (208/230 1ph). Minimum circuit ampacity for a water to air unit is about 17.5.
J

I did not know if they used a smaller compressor or they were set up for lower pressure with having a close water to air temp.

I was able to find 2 geothermal contractors that were willing to come out and bid.

Offgrid, your biggest headache may be startup current...same as locked rotor amps. Many similar geo units use same Copeland compressors. They can be coupled with a soft start option variously named Intellistart or Securestart. Supposedly they reduce startup current by 2x or more, but I can't vouch for one personally.

I should be fine with the locked rotor amps of the compressor. Adding a soft start cap and or timer would greatly reduce the needed start up amps.

I found a contractor that has gotten in touch Climate Master for what they will suggest on there scroll compressor.

They may suggest this (if they don't, tell them about this):

http://www.climatemaster.com/index/res_lit
Scroll down to "Emerson Secure Start"

The Water Furnace soft start is called IntelliStart.

Thank you.
I emailed him your response.

3 bids for mini split systems

Depending on your heating and cooling needs (location) you might want to reconsider the minisplits for off-grid. They can draw as little as 700 watts or less loafing along on partial loads. In my passive solar build, they are used to provide backup heating and cooling to limited areas at night when the only reliable power is the battery bank. You might want to consider how much of a shoulder season you will have during which you won't need full capacity. The minisplits with inverters can modulate themselves quite well, but the Copeland is limited to stage 1.

Don't forget to consider the current draw of the loop pump and the air handling fan of the geo system, both of which have to run whenever the heat pump runs.

Posted By ICFHybrid on 12 Jul 2011 12:13 AM
...but the Copeland is limited to stage 1.
Don't forget to consider the current draw of the loop pump and the air handling fan of the geo system, both of which have to run whenever the heat pump runs.

Last time I checked, dual stage 2-ton geothermal systems are available.  This would provide approximately 1.34 tons in first stage (2 x 67%.)  We have one installed on our second floor and it runs very well in both stages.

Also, there is no separate air handler required for a packaged geothermal system.

Last time I checked, dual stage 2-ton geothermal systems are available.

"limited to stage 1" means it can't go any less in low demand situations.

Also, there is no separate air handler required for a packaged geothermal system

It still has to run a fan capable of moving air for the full system capacity. That requires current.

Posted By ICFHybrid on 12 Jul 2011 08:45 AM
"limited to stage 1" means it can't go any less in low demand situations.
It still has to run a fan capable of moving air for the full system capacity. That requires current.

I don't recall anyone stating that stage 1 was variable.
Geothermal specs show kW usage at a given airflow.  Are you implying these specs don't include blower power or that power for an ECM blower in general is significant?

I don't recall anyone stating that stage 1 was variable.

Exactly, Gomer.

ECM blower current is low and increases slowly - not a significant design issue compared with compressor start.

A 2 ton package unit in low stage with favorable water conditions can (borrowing a phrase) "loaf along" at 1000 Watts or so

Posted By ICFHybrid on 12 Jul 2011 09:41 AM

I don't recall anyone stating that stage 1 was variable.

Exactly, Gomer.

As usual, clear as mud.

What was your geothermal experience again?  Fixed any systems with trees recently?

I'm adding information but remember my terminology is in manufacturing and not construction.

2 adults and one kid (been to the doctor so if there is more something is wrong).

New house under construction in SW VA. 2 bedroom, 1 bath, open kitchen/family, 835 sq feet with unfinished basement second bath don't care if this bathroom is heated or cooled (2 walls on the concrete will be insulated).

Walls are 2x4” on 16” centers, half inch of plywood, 2” rigid foam, half inch OSB, and the outside finish will be brick. This should give me a R-13 with a R-10 Barrier layer.
Windows will be dual pain double hung (coated / high performance glass (or what ever they call it)) with storm windows.
Exterior doors steel foam filled with screen/glass door.
Attic R-19 fiberglass and planning topping it off with blow in (I hate blown in insulation) looking about R-50.
Floor R-30 fiberglass.
If I go with a central HVAC or geothermal system I’ll box in main truck and insulation before heating session.


My wife decided to move our RV away form my office so I don't have access to the Manuel J and all the information in the bid. We should end up at home base latter this week.


I'm not sure about the mini split systems. The bids look over sized.
2.5 ton outdoor with 5 indoor units.
Dual 1.5 ton. One for the kitchen/family room. One for the bathroom and 2 bedrooms.


I thought Climate Master had a 1.5 ton Tranquility 20 (TS-018) and the smallest Tranquility 27 is a 2 ton (TT-026). It is 12,000 BTU to a ton right?

The bids look over sized.

Maybe they are oversized to get you more indoor units and more detailed temp control. Depending on your heat loss calcs, it might be right during winter lows. The cost of the mini splits including ease of installation has got to be lower than the cost of a full geo system.

Posted By ICFHybrid on 13 Jul 2011 01:04 AM

The bids look over sized.

Maybe they are oversized to get you more indoor units and more detailed temp control. Depending on your heat loss calcs, it might be right during winter lows. The cost of the mini splits including ease of installation has got to be lower than the cost of a full geo system.

ICFHybrid, it's amusing that when a poster comments about mini-split quotes looking oversized you contend that there "maybe" a reason for it and it "might be right", HOWEVER when a poster comments about geothermal system quotes looking oversized you contend it's deliberate to line the pockets of the corrupt geothermal installers. 

Looking for Gomer - check your mirror.