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Heat Pumps - Best practice
#1
Hi,

I wonder, what is the best practice to define heat-pumps that are used for both heating and cooling?

When one want to
1)    Capture the differences in efficiency when producing space cooling from when producing space heating.
2)    Capture the input of ambient heat and electricity (or gas).
(More important to capture difference in efficiency due to outputs, then to capture efficiency variations due to outdoor temperature for same output).
 
Thank you in advance for the guidance
Anna
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#2
I am not sure about best practices, but capturing the difference in efficiency due to outputs is easy in TIMES.  Just define ACT_EFF(ci) on each of the output flows, and then the efficiency will be ACT_EFF(c1) when producing c1, ACT_EFF(c2) when producing c2, etc.

For capturing efficiency variations due to outdoor temperature for same output, I have no solution. But if you can assume a certain outdoor temperature for each timeslice, then it is easy. Just define ACT_EFF(ci,sj) on each of the process flows ci and timeslices sj.

Capturing the input of ambient heat and electricity (or gas) should also be easy. You could define the efficiency (COP) for the purchased energy input, and define ambient heat as an auxiliary flow.  Then define the input flow of ambient heat to be equal to the output minus the input electricity or gas, e.g. by using FLO_EFF. As a result, the total energy input would be equal the total energy output, which I guess is the normal assumption when accounting the ambient energy input.

However, for demand devices (in-house heat-pumps), the optimal shares of the outputs (heat vs. cool) can usually be determined "beforehand", and thus the output shares can be assumed fixed. And because the demand load curves and efficiencies are also all known, all the levels of the process flows can be derived in terms of the annual activity.  In that case it might be easier to simply fix the output shares (and input shares, if the efficiencies are differentiated by timeslice) to those optimal shares. If the efficiency can be assumed the same over timeslices, you could then define only a single efficiency ACT_EFF(NRG,ANNUAL) for the process, and the model results will remain the same. If the efficiency is differentiated by timeslice, fixing the input flows by timeslice gives the correct flow levels.

[Edit: Clarified the last paragraph]
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