VRF HR (Heat Recovery) simulation with TRACE

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Dear Colleagues,

There is one issue, for which I still can't find the right way to model it with TRACE.

This is VRF HR (Heat Recovery). Actually the problem is the results seen on the reports and visualization charts. After longtime reading, checking, training courses..., I believe I've started to build the system up (to enter the data) as TRACE requires: Backup heat source (el. resistance), heat rejected to heating plan, etc. Also the outdoor unit was set up to operate till 0 OF as per the project.

VRF HR (air cooled) system in its performance, not only operate as heat recovery, but also operates like heat pump (either only heating or only cooling). This is because as per its construction (Daikin, Mitsubishi, and all the rest) the ratio of indoor to outdoor capacity is referred to as "combination ratio" and manufacturers allow combination ratios that exceed 1.0.

Being acquainted with these VRF HR specifics, I was expecting from the reports and visualization charts to see exactly such performance. Even kind of indication that Backup heat is not activated, because of condenser outdoor air was set to 0 OF.

My Question/Request is: What should be done in order to see such performance in the reports.

If TRACE is not structured to show this, advice please from your experience how to present the results, so that they illustrate that VRF HR is simulated.

From CDS told me that I have a misunderstanding of what VRF HR and what VRF Heat Pump is. After continuous communication, at the end they told me, that what I was looking for is Heat Pump and should model it like Heat pump.

Looking forward to your replies,

Best Regards

Vassil Vassilev


Vassilev's picture
Joined: 2012-05-23
Reputation: 0

Hi - I'm not sure if I'm going to be able to answer you're question.  However - I can comment on one thing I have seen with modeling VRF systems in Trace.  There is a fundamental misunderstanding of how VRF's operate within Trace.  It took me a few conversations with CDS Trace to realize this - but Trace inaccurately sends the heat that is rejected when the VRF's are in cooling mode to the boiler loop.  I was having an issue where a building I was modeling wasn't showing any gas consumption and it was because I had a VRF system and a boiler.  The boiler was heating part of the building and also serving as backup to the VRF.

What you have to do is create a second boiler plant and assign the VRF backup heating to that boiler plant.  When I reassigned the VRF coil to this new fake heating plant - all of a sudden I got realistic results.

Like I said - not sure this answers the question but your question made me think of the issues I've seen with VRF modeling in Trace.

Pearlyp's picture
Joined: 2012-08-09
Reputation: 2

Actually, that method is pretty essential for all heatpump type systems.
The reason for the "flaw" is actually just because of the way TRACE assigns coil loads. It can only assign a heating load to a heating plant, and then the cooling plant must be set to look for that heating plant. I just did a long bit about it in the TRACE training online because so many people ask.

However, I think your explanation is pretty good. I wouldn't say that it is innacurate. That's the way it has to work in TRACE because of the hard-coding that doesn't allow for heating coils to be assigned to a cooling plant (even if the said cooling plant is capable of heating)

Bob's picture
Joined: 2010-06-30
Reputation: 475