Variable Speed Ground Loop

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Hey All, Happy Friday,

I am trying to get a better feel for the control options available for
variable flow through a geothermal ground loop attached to water-cooled
heat pump units. Any comments would be greatly appreciated.

In eQuest, there appears to be only an option for an isolation valve at the
system level with no option to select 3-way or 2-way valves. This makes
sense because allowing for variable condenser flow would make the eir
curves with respect to entering condenser temperature invalid. By
selecting an isolation valve, I would expect that on an hourly basis, the
valve can either be fully open or fully closed. With this in mind, I would
expect the annual pump consumption to be equal for "Head Setpoint Control"
= "Fixed At Coils" and "Head Setpoint Control" = "Valve Reset". However, I
see that there is lower consumption with the "Valve Reset" strategy, which
leads me to believe that DOE2 is treating the valves as two-way. Also, an
hourly report of the condenser water flow through any unit shows that the
flow is not always 0 or the design flow but is often at an intermediate

Here are my questions: Can anyone confirm that DOE2 is assuming a two-way
valve by default? If so, how does DOE2 control the valves? Is there a
hidden keyword that would allow for a three-way valve? Does DOE2 account
for higher compressor consumption at reduced condenser flows?


Aaron Powers2's picture
Joined: 2011-09-30
Reputation: 0

I can only answer one of your questions, but that is that selecting "No" on
your isolation valve is the equivalent of having a three way valve. Per
the DOE-2 Help file:

NO The unit does not have an isolation valve. Full flow occurs whenever the
loop pump is active.

I would guess that DOE-2 is not accounting for increased compressor energy
at lower flows. If you look at the Performance Curves under the Unitary
Power tab there is no curve that uses condenser flow as an input.

Robby Oylear's picture
Joined: 2011-09-30
Reputation: 202

One normally associates air source heat pumps with DX cooled
systems. But I notice that you can select HEAT-SOURCE = HEAT-PUMP
for systems I would normally consider hydronic. For example a VAVS
system which only allows hydronic cooling allows the option of Heat
Pump for heating. Would this be a common practice in construction?

It is more hypothetical than actually wanting/needing to model this

>> Christopher Jones, P.Eng.

Chris Jones's picture
Joined: 2011-09-30
Reputation: 0


With over 35 years in the HVAC installation & maintenance feilds I have never
seen a system that incorporates a heat pump and hydronic cooling. Defeats the
purpose of a heat pump.

Paul Diglio, CEM, CBCP

Paul Diglio's picture
Joined: 2011-09-30
Reputation: 400