Re: [TRNSYS-users] COP curve inconsistency WW-HP

Hello Jeff,

First, thanks for the answer.

I isolated the heat pump into a new project, created 2 equation components representing source and load side flow and inlet temperatures but the heat pump is still having quite strange COP results, and I have no idea why.

Here is basically what I did:

Timestep: 0.1h

Type 927 (parameters 15 to 18):

rated heating capacity 177kW

rated power: 46kW

rated load/souce flowrate: 9.5 l/s

I attached my expected performance curve according to the performance data from TESS library for type 927, and the results from some of the tests I performed.

The main thing that I don't understand is why, even on the test project, there are so many scenarios that is in direct conflict with the performance data sheet.

By reducing the load-side flowrate and increasing the EWT for the load-side, the heating COP went to above 5, when according to the performance curve, both scenarios should decrease COP.

By having load-side EWT of 20 degrees C and flowrate equal to the rated value (9.5 l/s), the COP was near 3. By decreasing only the flowrate, COP increased to almost 4 (again, against performance curve).

And last, by decreasing source-side EWT, COP increased as well, when it should decrease.

Am I misunderstanding the system? Or I made a mistake even on the test project, as well?

On my main project I have a storage tank added and there are no errors during the simulation. I think my only problem is understanding this COP curve.

Thank you again,

Vitor L.

From: Jeff Thornton <thornton@tess-inc.com>
Sent: Monday, August 5, 2019 11:20 AM
To: TRNSYS users mailing list at OneBuilding.org <trnsys-users@lists.onebuilding.org>
Cc: Vitor Leite <vitorleite95@hotmail.com>
Subject: Re: [TRNSYS-users] COP curve inconsistency WW-HP

Victor,

The best thing you can do to start is to isolate the heat pump in a separate project and drive it with various inlet temperature and flow rates to make sure the performance of the machine matches the map. When you’re sure it’s working correctly that’ll help you track down what’s happening with the rest of your project.

Jeff

Sent from my iPhone

On Aug 1, 2019, at 10:24 AM, Vitor Leite via TRNSYS-users <trnsys-users@lists.onebuilding.org> wrote:

Hello everyone,

I got the results from a simulation and I think I am getting inconsistent results when comparing the heat pump COP and comparing it normalized performance data sample included with the component, which is the one I am currently using (type 927).

The system is basically two identical heat pumps (50RT) being controlled by a multi-stage differential controller. (which is also controlling the flow rate for both source side and load side pumps). So for the load side (connected to a vertical heat exchanger) there is only really small changes in temperature and the flow-rate goes from 0 to 0.5 to 1 following the number of H.Ps on.

Load side flow-rate also goes from 0 to 0.5 to 1 but there are bigger temperature changes according to the demand.

But, according to the performance data, during heating mode, the load side flow-rate should no change normalized capacity and if the load side temperature increases, normalized capacity should decrease. Which was not what happened with my results.

Can someone with a better understanding about H.Ps take a quick look and see if this graph is reasonable compared to the performance curve?

Thanks in advance

<COP.jpg>

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