RE: [EnergyPlus_Support] VRF heat recovery mode

Dear all,

Further to my previous questions:

E+ v7.2 also includes the option of water-cooled condenser. I guess for water-cooled VRF system, the performance curves used for the indoor units and outdoor units must be different from those for the air-cooled VRF system? If so, are there any such performances curves available for the water-cooled VRF units? And how can I get them?

Thanks again,

Dongyi

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: xiaodongyi@xxxxxxxxxxx
Date: Fri, 2 Nov 2012 21:24:06 +0000
Subject: [EnergyPlus_Support] VRF heat recovery mode

Dear E+ support team,

I am glad to know that the VRF model has been extended to cover heat recovery mode in the latest v7.2 release.

However, after reading the information regarding the VRF heat recovery model in the E+ Engineering Reference, I am still having some questions on how this is modelled in E+:
1. From the documentation in the Engineering Reference, it seems the VRF outdoor unit's operating mode (heating or cooling) is determined by the dominant load, which is determined by the master thermostat priority control. Looking at the options for the master thermostat priority control in the input/output reference, it looks to me that the VRF outdoor unit's operating mode will be determined by:
a) the greater required VRF system load, i.e., if the required heating load from the indoor units on a VRF system is greater than the required cooling load from the indoor units on the same VRF system, then the outdoor unit will be forced to operate in heating mode. In this case, what if the outdoor unit can still work in cooling mode, and with the required cooling load, taken into account the compressor power, that the outdoor unit's heat rejection load can satisfy the required heating load on the system? Idealy, this would result in a totally balanced heat recovery, I think?
b) the zone load where the master thermostat is located. This again does not quite make sense to me since we don't know if this is going to make full use of the possible heat recovery between the terminal units working in heating and cooling mode.
c) the number of zones requiring heating or cooling.
d) the zone fartest from the thermalstat point.
Again, I have the same question for c) and D) as that I have for a) and b).
2. I wonder if this heat recovery mechanism implemented in E+ is an appropriate model for the real heat recovery control used in the VRF system. -- Is there any information on the testing/validation about this VRF heat recovery model?
3. the Engineering Reference states there is a modelling for the transient period from heating only or cooling only mode to the heat recovery mode, using the exponential equations. Is there also a modelling for the transient period from the heat recovery mode to the heating only or cooling only mode?

Thanks in advance for your much appreciated help to answer my questions,

Dongyi

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