[Equest-users] FW: Custom curves - Loop to Loop Heat Pump

[Molly Curtz]

Ana,

As I read the help files, I believe you are correct that you need to develop only one set of curves which governs the equipment operation for both heating and cooling. I've not developed custom curves for this chiller type, but I have a couple thoughts that might be helpful.

One suggestion is to dig into the hourly chiller reports. I think you will see a set of variables with the phrase "chiller/heater only" in the variable name.( I say "I think" because I recently looked at the reports for a "Heat Pump" chiller (not a "Loop to Loop Heat Pump" Chiller.))
These variables seem to report on the heating mode operation of the "chiller." One is titled, "Electric Heat Use, Heater/Chiller only." I am not clear what "Electric Heat Use" would represent: I think this is likely the kW power consumption in heating mode operation?

Hopefully, there is also a report variable which tells you what "mode" the equipment is operating at - there are 4 modes of operation as described in the eQuest help for "Loop-to-Loop" chiller type

You can calculate and spot check the kW/ton that the chiller is operating at, by digging into these reports and doing some calculations on the data. There are also report variables which show the what eQuest calculated for the adjusted EIR, so you can check against what you think it should be from your curve coefficients.

Another thought is to examine the default curves provided for the "Loop to Loop Heat Pump" in eQuest. Pull the coefficients from the performance curve properties and graph them in excel (fix one of the variable so you can do it in 2D.) Doing some comparisons with your curves might help you figure out the situation.

One thing I've noticed when looping into this is the variable "MIN-COND-T" (in eQuest under Chiller Properties: Condenser tab.) In cooling mode operation this seems to limit the minimum condenser temp - check the hourly report on "Condenser entering temperature". For a ground loop HX system, the default value (of 70 F) seems high, since the ground source loop would often be below this temp. I'm unsure how to interpret this -it's something I've noticed but not delved into.

Regards,


Molly Curtz
Mechanical Engineer

Arup
403 Columbia Street  Suite 220 Seattle WA 98104
t +1 206 749 9674  d +1 206 493 2234
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www.arup.com

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Ana N.
Sent: Thursday, September 30, 2010 6:58 AM
To: cmg750 at gmail.com
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] FW: Custom curves - Loop to Loop Heat Pump

Carol,

DOE22Vol2-Dictionary_47b, pages 220-221 indicate that only one curve should be used. That is why I tried creating only one curve. I assume we should create one curve EIR= t ( t evaporator leaving, t cond entering). It is relatively simple for the cooling mode. In the heating mode, the evaporator leaving temperature is actually the source fluid leaving temperature (manufacturers typically provide the data for the source fluid entering temperature), while the condenser entering temperature would be the load fluid entering temperature (manufactures typically provide the data for the load fluid leaving temperature). Do you agree with this rationale? Unfortunately, I do not like much the results I got.
DOE22Vol2-Dictionary says that curves should be normalized at the Eurovent rating condition, rather than ARI.

Thank you

Ana


________________________________
Date: Wed, 29 Sep 2010 18:49:39 -0700
Subject: Re: [Equest-users] FW: Custom curves - Loop to Loop Heat Pump
From: cmg750 at gmail.com
To: ananeddav at hotmail.com
CC: equest-users at lists.onebuilding.org

Hi Ana,

As always it would be good to see what you are looking at so if you feel comfortable sending your .inp and .pd2 files please do. I'm not sure why the HIR field is grayed out but I can understand why 2 HIR curves would confuse eQUEST. You will have to do a parametric run or just run your model twice, once with one curve and again with the other curve. Also, be sure to read the information about curves and curve inputs in the DOE2 manual. All the data needs to be normalized around the ARI conditions and the ARI conditions always equal 1.0. It can be confusing at first.

Good luck!

Carol
On Wed, Sep 29, 2010 at 2:29 PM, Ana N. <ananeddav at hotmail.com<mailto:ananeddav at hotmail.com>> wrote:

Dear e-quest users,

I am modeling a central ground source heat pump that provides both cooling and heating by using the Loop to Loop Heat Pump. I am trying to derive the performance curves based on a very detailed set of data provided by the manufacturer. What confuses me is that HIR field under the performance curve tab is grayed out.

I have derived one curve by combining the performance data  for cooling and heating mode (by using methodology described for chillers, "Tools and Techniques to Calibrate Electric Chiller Component Models<http://www.taylor-engineering.com/downloads/articles/ASHRAE%20Symposium%20AC-02-9-1%20Electric%20Chiller%20Model-Hydeman.pdf>, ASHRAE Symposium" ). I am not sure this is the correct approach. Should I create one EIR curve by combining the data for cooling and heating (EIR= f(T evaporator leaving, T cond entering) and leave HIR curve "grayed out"?
I also run the model with two separate curves
EIR= f (T evaporator leaving, T cond entering),
HIR= f(T evaporator leaving, T cond entering),
each derived using the performance data for corresponding mode of operation.
 However, when I run the model with two different HIR curves, the result remains unchanged as if e-quest does not use this curve at all.
At this point, I am using default EIR=f( part load). I am still using e-quest 3-63.

I would really appreciate sharing your experience in modeling the Loop to Loop Heat Pump and deriving custom curves.

Thank you

Ana


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--
Carol Gardner PE
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