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  1. #1
    Join Date
    Mar 2001
    Location
    Washington DC
    Posts
    73
    Hi Folks:
    I have several jobs that I am looking into geothermal for. In each case, they are not particularly large loads, often only 3-5 tons total, but they would be easier served by two air handlers. So it would be two rather small units.

    I know of several options, I'd be interested in hearing thoughts/experience.

    One is multiple self-contained units running off a single geoexchange loop. I wonder if anyone ever plumbs the geoexhange loop as primary/secondary loops, to eliminate the pressure drops through all the exchangers if the units are in series? I'm not sure it's worth it for only two units, and of course there are the additional pumps and controls.

    Another option is to put in a single water to water GSHP, then put in air handlers with coils (a chiller approach). Problem is the hot/cold lines that have to snake around the house, and associated heat loss/gain (common enough commercially, not often residentially). Another problem is that the ground source heat pumps don't like cranking out very hot water (about 130F max).

    In some cases there's a desire to integrate radiant floor hydronic heating into the equation. A water to water HP would make that easier. It would also make integration of an indirect water heater operating off the heat pump easier (vs. a desuperheater, that can only take care of your hot water loads during system operation, and therefor only reduces DHW energy use by 30% or so). I believe Hydro Delta has something like this integrated into some of their units, though I don't have many details yet.

    Thanks for any thoughts and ideas.

    Warmly, Keith

  2. #2
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    The 2 zone units I have done have had the geo water loop connected to the units in parallel. The only trick to this is if there is a major size difference between the two units, or if they are separated by a significant distance, a flow control valve may need to be added to balance the flow between the two units. I have done 1.5 and 2 ton as well as 2 x 2 ton on the same loop, with one circulator. You need some sort of control relay so that either unit will run the circulator. ClimateMaster sells a small, inexpensive solid state control for the purpose. I use a single DPDT 240 v coil relay, mounted in a small pull box. The relay is cheaper and a simple install.

    As for radiant with geo, it does a nice job with 120 deg water. Only hassle is with selector (zone) valves to select radiant heat or chilled water to an exchanger in the air handler. For sure radiant is costlier, but if the customer wants it, go for it. Compared to the loop costs, the added money for radiant is not that much over a gas or oil radiant system.

    paul

  3. #3
    Join Date
    Apr 2006
    Location
    Nebraska
    Posts
    115
    We have had similar situations, and have opted to zone the duct system with one geo unit. If two units are used, I personaly like two seperate loops. However it is much cheaper to run one field on two system and it does work just fine.
    "Egotism is the anesthetic that dulls the pain of stupidity."
    Frank Leahy

  4. #4
    Join Date
    Mar 2001
    Location
    Washington DC
    Posts
    73
    Thanks for your thoughts. There are some complications: in one of the houses, the radiant would only be for a portion, so we'd need some hot air too. In several cases, ducting the whole house from one point seems really difficult, it would just be easier having one air handler in the basement and another in the attic, with basement/1st and 2nd/3rd coverage. As for the DPDT relay, that would be easy, I just put in a priority DHW relay box for an oil boiler with two radiant zones and indirect DHW, so I'm not concerned about that part... I don't know anything about flow control valves and the like, on the other hand. I gave some thought to the idea of parallel vs. series pumps, since in series the second pump would always have to deal with a higher EWT (when the first unit is operating), but figured that if the loop were sized properly loop temp would still be within bounds, and it seemed simpler to either do single series loop or primary/secondary arrangement. Anyway, thanks for your contributions!

    Keith

  5. #5
    Join Date
    Mar 2003
    Location
    PA/DE area
    Posts
    1,535
    we install hydro-delta and the quartro-therm with great results.
    It's NOT the BRAND,it's the company that installs it!!!!!

  6. #6
    Join Date
    Mar 2001
    Location
    Washington DC
    Posts
    73

    Hydro Delta & Quadro-therm Dual stage compressors

    I notice the H-D Quadro-therm has a two-stage reciprocating compressor that runs backwards with one piston or forward with 2 to vary the output. I guess they call it the Megatek TS technology.

    I have a general impression of scroll compressors being more reliable than reciprocating. On the other hand, they avoid requiring two compressors for a two-stage system...

    How reliable are these compressors?
    How noisy are they?
    Have they been/are they used on other systems? Seems like if they worked well they'd be used on air-source systems as well, since multi-stage (mode?) compressors/systems with ECM fans seem to me to have a very desirable flexibility for variable climes.

    thanks as always for the insights and information!

    keith w

    PS: Wow, how convenient that they schedule their service calls in advance!

  7. #7
    gto boy Guest
    I do not think they are noisey,I have a MEGA TEK which is the same but no desuperheater.

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