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Water condenser low temperature, chiller heat recovery

asked 2017-06-20 05:26:07 -0500

Gio gravatar image

updated 2017-06-20 08:37:43 -0500

Hi, I'm trying to model a chiller with heat recovery, for DHW purposes.

I'm using a Chiller:Electric:EIR connected to a WaterHeater:Mixed. The model is running but I get a very low water temperature from the chiller condenser. Basically the water going into the tank water heater is decreasing its temperature since the inlet water temperature goes from 30°C to 20°C.

How can I get an higher temperature from the chiller condenser? Did anyone have the same issue?

I found something here: https://unmethours.com/question/19434...

Thank you in advance

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answered 2017-06-20 14:14:41 -0500

Heat recovery from the Chiller:Electric:EIR object is applied through two nodes:

These nodes are meant to be connected to a heat recovery loop (where your water heater is located) that is separate from the condenser loop. It sounds like you're trying to connect the water heater to the CONDENSER inlet and outlet nodes instead, which you should not do.

You can find a schematic of an air-cooled heat recovery chiller in the second image of this article, but I will note that heat recovery from the Chiller:Electric:EIR object is only available for water-cooled chillers according to the last sentence in the description of the Design Heat Recovery Water Flow Rate input field.

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I'm using DesignBuilder, I think the connection is right: https://www.dropbox.com/s/13mi897zrqh...

I adjusted the water flows and the design temperature of the HR loop, the condenser loop and the Auxiliary loop and also the design leaving condenser temperature of the chiller.

I got a better result (https://www.dropbox.com/s/85uggnbs4xz...), now the leaving chiller condenser temperature is about 30°C so the Tank temperature is between 28°C and 34°C. Unfortunately, the condenser loop is still working even if the tank setpoint temperature is not reached.

Gio gravatar image Gio  ( 2017-06-21 06:17:33 -0500 )edit

@Gio, it does look like your connections are right. The heat recovery loop is working correctly and providing some heat from the chiller to the water heater, but there is still heat that must be rejected from the chiller to the condenser loop. That is why the condenser loop operates even when the tank setpt temp is not reached.

Currently, the 30C heat recovery water won't help the water heater achieve a typical >50C setpt temp. You may want to consider connecting the heat recovery loop to a storage tank without a heating element, then provide water from the storage tank to the water heater.

Aaron Boranian gravatar image Aaron Boranian  ( 2017-06-21 11:22:39 -0500 )edit

I'm sorry I didn't understand your last sentence. Do you mean with 2 different WaterHeater:Mixed? I think I would still need to connect the second one to another generator to integrate the remaining heat to reach 50°C

Gio gravatar image Gio  ( 2017-06-21 11:36:30 -0500 )edit

Correct, there would be two WaterHeater:Mixed objects: one with no heating capacity (max and min heating capacity set to zero) and source side nodes connected to the heat recovery loop, and a second with heating capacity and source side nodes connected to the first water heater. If the heating capacity of the second tank is large enough, it should be able to provide 50C water without another auxiliary heater or generator. Sorry for the confusion.

Aaron Boranian gravatar image Aaron Boranian  ( 2017-06-21 11:46:06 -0500 )edit

No confusion and thank you very much. I'm going to try it as soon as possible!

Gio gravatar image Gio  ( 2017-06-21 11:49:14 -0500 )edit

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Asked: 2017-06-20 05:26:07 -0500

Seen: 99 times

Last updated: Jun 20 '17