I was reading another topic and the tought occured to me, what is the difference with units of different tonage (BTU output).  I would assume that a Gas system would have additional burners, more surface area and a bigger blower as the tonage of the systems become bigger and the same would be true with oil and propane systems.  So how are Goethermal systems different as tonage increases?  Besides the obvious of a larger blower, whats bigger on a larger geo system?  Does the water flow thru a larger system faster?  Is the heat pump larger? Are the more heat transfer loops?  More surface area for the exchanger?  If the exchanger is the key, what pervents you from putting a larger exchanger / blower on a smaller heat pump?
 

More gpm flow, larger compressor, larger fan coil, larger coax, heavier, physically larger cabinet and larger duct and electric demands.

That pretty well covered it except they cost more also.

What about the part that is in the ground?

Regards,

Masoud

Ground part is sized in direct portion to unit capacity.

I thought ground exchangers were sized based upon loads. . . .  (or that they should be sized based upon loads). 

Unit capacity is sized for loads, the loops follow.

Off topic, but our HVAC suggested that if we were going to run the geothermal in an off peak situation only (14 hours a day max) he would upsize the compressor by 1.5 tons, but keep the field the same size. The reason he gave was we were going to take the same BTU's out in 24 hours, but take it out in less time. I said ok, but then we ended up increasing the field size to match the heat pump size.

I'm sorry I don't know what this means....
joe

This might work if a geothermal system heated a house up and the house stayed that way temperature all day, or in your case for 10 hours before the system can flip on again at off peak power hours.  But a geothermal system doesn't work that way, it heats up the house and maintains the set heating level.  The only way I can see this working as stated is to heat the house up well above your ideal temperature and as the house loses heat over 10 hours, to keep it above your ideal temperature before it can flip on again during off peak power usage hours.  And if turning your heat up involved the AUX heating strip at all, throw all those savings, if any out the windows. What your left with will be wildly fluctuating house temperatures, instead of a nice even temperature.

Sounds like to me you wasted money by over sizing the system and the ground loop. I can't see how this will ever work for a off peak ONLY situation.   

I think I understand, but it'll only work well with a high thermal mass house. In other words, the mass of the house carries you through the interval when the power is off to the heating unit.

However, I doubt a significant upsize is called for. The effect of a high mass house is to carry heating or cooling load forward into milder times of day. Daily runtimes increase beyond what is experienced in a stick built house. A smaller unit runs much longer. Heating loads carry into late morning, cooling loads deep into the night. This is good for comfort.

In an odd coincidence I recently deliberately derated my open loop system for several days during which outside temps wee below design day in order to produce very chilly water for a snow gun. I pinched down the flow to chill 71 deg well water to 40 or so rather than the typical 55. Result was greatly increased run times (18-22 hours per day) but no significant dips in house temps - basically kept 72 the whole time. I'm quite certain a stick house would have experienced significant late night dips in temps under this scenario.

If memory is good, Brock mostly uses pool water, geothermally heated off peak, in radiant heating during winter.

Regards,

Masoud

16k gallons of pool water is a LOT of thermal mass!