RE: [EnergyPlus_Support] Free cooling with chiller

Jean,

That’s what I’m looking for.

I’m trying to simulate a system which uses a cooling tower at night, to cool the zone in free cooling modus with water at 17°C.

At day the chiller is used to have this water temperature.

In Designbuilder I can use two chillers, one with a day and one with a night schedule, the last one connected to a cooling tower.

Nevertheless, I’m not sure if I can use free cooling as such, as I still have to pass the chiller. Connecting the tower directly to the chilled ceiling is not possible I assume.

Best regards,

Geert Bellens

Van: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] Namens jeannieboef@xxxxxxxxx
Verzonden: vrijdag 6 december 2013 9:05
Aan: EnergyPlus_Support@xxxxxxxxxxxxxxx
CC: EnergyPlus_Support@xxxxxxxxxxxxxxx
Onderwerp: Re: [EnergyPlus_Support] Free cooling with chiller

That is a common scenario. I'm working on a real project right now where the chiller is bypassed completely (chiller off) by the economizer loop using the chiller dryfluid cooler on the roof to cool the chilled water loop. The "economizer mode" kicks in at ODAdrybulb less 10 deg C. As building cooling loads during these times are much less in any event, the much higher chilled water loop temperatures still manage to supply AHU and Fan Coils with water cool enough such that they can meet the loads. I'm simulating this project in TrnSys so don't ask me how I'm doing it.

Jean

On 05.12.2013, at 22:48, Chien Si Harriman <chien.harriman@xxxxxxxxx> wrote:

hi Geert-

What you are saying is technically possible. But the outdoor temperature would have to be quite cold. There are some air-cooled chillers on the market that I have seen which do this, but the outdoor ambient temperature must typically be somewhere below the freezing point of water.

As you know, you need a fairly large temperature difference to drive cooling cycles in general, so it must be quite cold. And controls are of course very important to prevent the water from freezing when exposed to such cold temperatures. I worked on a project in Budapest where this approach had been taken using air cooled chillers. I believe Carrier made these chillers. Here is a link to a sample chiller that is like this.

I had always thought this was possible as well, but I had never seen a manufacturer who had produced this type of machine. Now there is at least one that I know of. If the link does not work, the model is the Carrier 30XA 252-1702. This manual even includes the performance of the chiller under these conditions. I do not know if there is a water cooled chiller with this capability. As I said, controls are important. Maybe the water cooled chillers prove too difficult to control. I am not a chiller expert.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDcQFjAC&url="">

On Thu, Dec 5, 2013 at 11:38 AM, <geert.bellens@xxxxxxxxxxxxxxxxxxxxxx> wrote:

If you use the chiller , isn't it possible to do some 'free cooling' when the outside temperature is lower than the desired water temperature? (eg at night)

In theory the compressor doesn't have to do anything at that moment.

If I try that, I still get chiller consumption. even at low outdoor temperatures.
I use the ConstantCop chiller, maybe that's the reason?

Geert

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