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VRF with hot water generation, heat exchanger

asked 2017-04-24 08:53:27 -0500

Gio's avatar

updated 2017-05-08 16:10:12 -0500

Hi, I need to model a VRF system with a so called "Hydro Box". It is a plate heat exchanger that allow to generate hot water that can be used both for heating demand (ie heated floor) and for DHW demand. Therefore the system can produce heating with hot water AND with direct expansion coils (split).

I specify that this approach is considered in heating mode, so it's not related to a heat recovery during cooling (that I know it can be modeled).

So my question is: is there a way to model a condenser based on a "refrigerant to water heat exchanger"?

Thank you

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answered 2017-06-07 15:07:28 -0500

Yes, you can model this using the AirConditioner:VariableRefrigerantFlow object with the Condenser Type input field set to WaterCooled. You would then need to create a PlantLoop object for the water loop that will use the rejected heat from the refrigerant loop for heating demand and / or DHW demand.

It doesn't seem that there is a "plate heat exchanger" option, but you could represent that relationship using the various performance curve input fields.

Someone asked a question related to performance curves for water-cooled VRF systems, which you may want to check for reference.

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Thank you for the answer, that's interesting. This means you need cooling demand to obtain heat from the condenser, isn't it?

Therefore if it's cold and I don't need any cooling, I can't get DHW or heating.

Did I misunderstand it?

Gio's avatar Gio  ( 2017-06-08 09:23:06 -0500 )edit

@Gio - yes. You might want to look at the WaterHeater:HeatPump objects.

kwalkerman's avatar kwalkerman  ( 2017-06-08 10:52:38 -0500 )edit

@Gio You are correct, you would need cooling demand in the zones in order to have the refrigerant loop reject heat from the condenser to the hot water loop. When it's cold and zones have heating demand instead, the refrigerant loop will need to siphon heat from the condenser instead.

As @kwalkerman mentioned, you could use a WaterHeater:HeatPump object so that DHW system could receive heating year-round. However, this object doesn't provide space heating.

Aaron Boranian's avatar Aaron Boranian  ( 2017-06-08 11:08:43 -0500 )edit

@kwalkerman I think you can provide heating with it, but through a water coil terminal (fan coil for example). In this case I need a direct expasion to provide heating and cooling and a condenser for DHW. During winter (heating demand) I temporarly switch the power to the DHW generation; during summer instead, it reverses the cycle to shortly produce the hot water.

Gio's avatar Gio  ( 2017-06-08 16:44:06 -0500 )edit

@Aaron Boranian I think I could model both of them, 1 heat pump for DHW and 1 VRF for heating and cooling (basically it's one machine with 2 different operations thus different performances), but they shouldn't never operate together. Could it work? Can I set them not to operate simultaneously with DHW priority?

Gio's avatar Gio  ( 2017-06-08 16:46:15 -0500 )edit

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Asked: 2017-04-24 08:53:27 -0500

Seen: 632 times

Last updated: Jun 07 '17