[Equest-users] [Bldg-sim] loop to loop heatpump in equest
davidr at madisonengineeringps.com
Fri Jul 24 15:41:23 PDT 2009
One limitation of the Well-Water-to-Water Heat-Pump (or W2WHP, TYPE =
HEAT-PUMP) is that only a chilled water or 2-pipe circulation loop can be
attached to it. This can be an issue if the central heat pump is designed
to supply both hot and chilled water.
>From other BLDG-SIM and EQUEST-USER posts, for simulating WSWHPs that can
produce both hot and cold water simultaneously, I gather that analysts often
opt to use loop-to-loop heat pump (or L2LHP, TYPE = LOOP-TO-LOOP-HP)
instead, since you can connect both a chilled water and hot water loop to
the chiller. However, from experience, I know that many of the
water-to-water heat pumps available are NOT loop-to-loop heat pumps, but
rather a series of water-to-water heat pumps that are manifolded to allow
some circuits to operate in heating while others are operating in cooling,
with all circuits sharing a common condenser water loop. If you read the
description of the L2LHP chiller closely, the L2LHP operates much
differently than the W2WHP machine. Also, I would be wary of using the
default DOE-2 performance curves for loop-to-loop and well-water-to-water
chillers, as I found that the default performance curves were quite
different from what is currently available in the US market.
The approach you have outlined, I believe, is on the right track, if the
correct chiller type is being simulated. However, it seems unlikely that
estimating the ground loop loads/temperatures using a building model with
single-zone WSHPs will produce the same results as the W2WHP/chilled beam
system you described.
Here are some reasons:
1) Does not account for pump heat (both positive and negative impact
depending on it the system is in heating or cooling) on the building
circulation (chilled beam) loops.
2) Using the "DX/DX heating/cooling ground source heat pump" option you
mentioned, you will basically get single-zone WSHP systems, where the WLHP
loop is connected to the eQUEST GSHX (well-field) model. This method may be
taking too much credit for periods when there is high diversity in the
building. If a small fraction of the building requires cooling, the chilled
water system would have to run and the W2WHP would impart a load on the
ground loop and GSHX. However, in a building model with single zone
water-to-air heat pumps, I believe the load on the loop could, in theory, be
balanced by a fraction of units in heating and cooling, so that the ground
temperature leaving the building is the same as it was coming in.
3) Finally, part-load performance curves for water-to-air heat pumps
are likely not appropriate for a water-to-water heat pump system.
Here is a suggested alternative (that I have fully implemented in eQUEST):
1) Take the hourly LOADS on the lake/well loop model you have created.
2) Apply them, with the appropriate schedules, as a internal energy
source in a single space building.
3) This space is served by a single zone, water-to-air heat pump, which
has a WLHP condenser loop and a GSHX, as would be typically be created by a
4) Make all the surfaces of the space adiabatic, zero out all other
loads and the system fan energy, and set you cooling/heating EIRs to 1.0.
With a few other adjustments (not enough time to list them all), you can
more or less get the load on the WSHP loop to be the same as internal energy
source load applied to the space.
In essence, you are taking the loads directly from the lake-well loop and
transferring them to the other model what includes the GSHX model of the
well-field. From this secondary model, you can then extract the
temperatures returning from the well-field. The rest is similar to you
described, except you could even get as detailed as 8760 hourly load and
temperature schedules in each model.
Any thoughts from others who have simulated/studied these systems before?
Madison Engineering, PS
444 NE Ravenna Blvd, Suite 406
Seattle, WA 98115
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, July 24, 2009 11:09 AM
To: bldg-sim at lists.onebuilding.org
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] [Bldg-sim] loop to loop heatpump in equest
I've chatted with Rashmi and feel like others may want to know how this can
be done in the future... Also copying [Equest-users] on this discussion as
advised by a list administrator.
See attached screengrab for a simple visual of how I accomplished this...
Setting up the 4-pipe system sourced from a closed ground loop:
1. Create a 'chiller' of the type 'water-to-water heat pump'
2. Create an independent circulation loop of the type 'lake/well'
3. Create a ground loop heat exchanger of the type 'lake/well'
4. Select as the chiller CW loop and GLHX circulation loop the
independent loop you created - they should connect without errors
5. Assign a custom temperature schedule for the lake/well ground loop
in the screen that pops up when you double click the GLHX (read on)
6. Make sure the default head/pump properties for the circulation loop
and GLHX make sense for your system - adjust as necessary. (i.e. if it's a
closed ground loop, there shouldn't be static head)
The tricky thing is that both Rashmi and I were dealing with closed-loop
ground heat exchanger (not lake/well). The solution I came to model this
was to temporarily save the project in a separate directory to keep my work,
then go back to the wizards and heat/cool the same building reasonably using
the DX/DX heating/cooling ground source heatpump option, with all
appropriate ground and field properties well defined.
Once this is done, you can have eQuest additionally generate an hourly
report over of the resulting ground loop temperatures throughout the year
(actual procedure eludes my memory, but it's in the archives). Once this is
done, I used that raw data to come up with the resulting weekly average
temperatures in the ground loop using excel. I then used these figures to
create a custom temperature schedule for the actual project, which was
assigned to the GLHX as mentioned above. This way you're reasonably
accurately representing what temperatures the water-to-water equipment is
seeing coming out of the ground throughout the year based on your actual
geographic, ground loop, and soil condition variables as defined.
The final logical step, and one I'm currently working on learning for
myself, is defining a custom performance curve for the water-to-water
equipment that's representative of the real thing. I have been advised the
default chiller curves as well as the water-to-air heatpump curves from the
Climatemaster eQuest add-on are not appropriate for modeling water-to-water
Best of luck!
PS: Apologies for the screenshot's quality - I had issues making it small
enough for the mailing list to accept.
NICK CATON, E.I.T.
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Anthony Hardman
Sent: Friday, July 24, 2009 10:13 AM
To: 'Rashmi Sonal'; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] loop to loop heatpump in equest
Would the following get you close enough (ignoring the DOAS side)?
1) Specify a water-air HP system
2) Zero out the fan energy
3) Factor the load side pumping energy into the EIR of the HP
a. Alternatively, you could add your load side pump energy to the
source side pump
Obviously there's limitations either way and I've never tried this, just
thinking out loud. Certainly someone else out there can comment who has
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Rashmi Sonal
Sent: Thursday, July 23, 2009 3:39 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] loop to loop heatpump in equest
I am trying to model a building with water-to-water heat pump connected to
ground HX and 4-pipe AHUs with induction unit at the terminal.
I have specified induction unit at the terminal, to model active chilled
beams, with a dedicated outdoor air unit. But with this configuration on
airside I am not able to attach the water to water heat pump to any
condenser water loop on the water side. Is there a way I can model GSHP
serving active chilled beams in equest?
Thanks in advance.
Rashmi Sonal, LEED AP
Computational and Simulation Analysis (CoSA)
Tel: (+1) 212 616 0285
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