[Equest-users] Variable Speed Ground Loop

[Aaron Powers]

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
value.

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?

Thanks,
Aaron
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