[Equest-users] Not Meeting Heating Setpoint with Ground Source HeatPump

Nathan Miller nathanm at rushingco.com
Mon Aug 11 17:10:43 PDT 2008

You may want to check your heating schedule. I find that Heat Pump systems
have a hard time ramping up temperature quickly. If you set-back the
temperature at night, the system probably has unmet heating load hours
each morning when the system turns back on.

In the past I have been able to make the unmet load hours go away on HP
systems by modifying the heating schedule such that there is a several
hour transition from my nighttime set back to my daytime set point.

Nathan Miller

Senior Energy Engineer/Mechanical Engineer

direct: 206.788.4577

fax: 206.285.7111

-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Doebber,
Sent: Monday, August 11, 2008 4:17 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Not Meeting Heating Setpoint with Ground Source

I am using the Package Single Zone (PSZ) air system to simulate a Ground
Source Heat Pump.

For Cooling, the Heat Pump Condenser Coil is specified as "Water Cooled"
and linked the GSHP Water Loop.

For Heating, since there is no input for the Heat Pump Evaporator Coil,
I'm assuming that Equest automatically uses the GSHP Water Loop.

Everything works great except that for many of the Heating Mode Hours, the
system is not meeting the correct 70°F Setpoint Temperature.

The following HAS NOT worked :

1.  Increased "Heat Sizing Ratio" to 1.5 to oversize the Heating Capacity

2.  Added Electric Resistance as a "Zone Heat Source"

The following HAS worked :

1.  Specifying "Electric" as a HP Supplemental Source

There seems to be a control issue of either turning the Heat Pump off or
not running it correctly to meet the Heating Load.  I can maintain the
Temperature by using Electric Supplemental Heat but I want the Ground
Source Heat Pump to provide all the heating which it is capable of.

Any thoughts.  For instance, if I specify "Heat Pump" as my Supp Source,
will this simply use the GSHP to provide the heating.  Seems like an odd
way of doing it.


Ian Doebber
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