Modeling Indirect-Evaporative Cooling with Winter Heat Recovery

asked 2014-09-18 16:30:39 -0600

Anna Osborne Brannon

2937 ●8 ●25 http://www.atelierten.com/

updated 2014-09-30 09:42:41 -0600

Neal Kruis

4745 ●10 ●17 http://bigladdersoftware.com/

Specifically, do you use two components- a direct evaporative cooler (spray chamber) on the exhaust side and a heat exchanger, and if so, what efficiencies do you typically use? I am seeing one whole-system rating from manufacturers: about 70% (in the Bay area). If winter heat recovery has a lower effectiveness than the IEC rating, how do you set-up/control it? I am specifically using IES<ve>, but any general information would be useful, or how other softwares handle this system.

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answered 2014-09-19 00:35:59 -0600

Joe Huang
2772 ●5 ●14

updated 2014-09-19 00:59:31 -0600

It sounds like you're working with a single-stage indirect evaporative cooler that doubles as a dry heat exchanger for heat recovery in the winter. In that case, you should just model it as a single component with a certain effectiveness, which is the fraction of the total wet-bulb depression (Tdry - Twet). Most of the literature I've seen have default effectivenesses (?) of 0.85 for direct and 0.60 for indirect evap coolers. If you want to get a little more fancy, you could add an effectiveness curve that varies with the part-load ratio and wet bulb temperature. Back in the early 1990's, I worked with a Visiting Scholar from China (Prof. Chen Peilin) who developed a detailed indirect evaporative cooler model that he then used to calculate effectiveness curves for IEC precoolers that I then incorporated into the DOE-2 program see this paper. I'm sorry that I don't have digital copies of most of my evap cooling papers, but I do have the last one where I calibrated my models against PGE measured data here that might be of help.

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Thank you! I also found this page on from Big Ladder that helps with a lot of my questions: http://bigladdersoftware.com/epx/docs/8-0/engineering-reference/page-083.html

Anna Osborne Brannon ( 2014-09-22 16:03:55 -0600 )edit

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answered 2014-11-24 14:59:26 -0600

Lincoln

1521 ●1 ●11 http://www.kw-engineering.com/

updated 2014-11-24 15:07:31 -0600

I've modeled this before using OpenStudio. OpenStudio 1.5 or later offers a lot of flexibility by allowing direct or indirect evaporative coolers to be placed on the outdoor air exhaust/supply nodes. One option would be to place an indirect evaporative cooler on the supply node along with a HX coupling the exhaust and supply air streams. Another option would be to place the direct evaporative cooler on the exhaust stream with a sensible HX.

If you want to model a direct/indirect evaporative cooling system you could place a direct evaporative cooler on both air streams and couple the streams with a sensible HX. There is a measure that automates this available through the BCL.

For the indirect/direct evaporative cooling objects you can specify sensible and latent effectiveness's respectively. For the air to air HX you can specify both a sensible and latent effectiveness at various airflow rates for heating and cooling.

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@Lincoln, when modeling this system did you place a separate setpoint manager for the direct evap cooler on the exhaust stream? If so which one? I am just wondering if EnergyPlus will operate the evap cooler in the exhaust steam correctly without more input from the user.

TaylorRoberts ( 2016-04-11 17:27:21 -0600 )edit

yes, put a setpoint manager on the outlet node of the direct cooler. The direct evap cooler in E+ has a field to input the Sensor Node Name. I think OpenStudio fills this input in for you but I would double check...

Controlling the direct cooler in different conditions may be difficult so you could also look at using an indirect cooler on the outdoor air inlet stream.

Lincoln ( 2016-04-13 10:53:20 -0600 )edit

Hi, @Lincoln i tried adding an HRV after the IEC on the supply side but what I want is that the HRV only works when the IEC doesnt work in wet-mode. Is there a way to control the HRV so specifically? I believe only then we can truly use the HRV only for winter Heat recovery below a temperature when the IEC shuts off.

AnmolMathur ( 2021-09-24 06:57:43 -0600 )edit

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answered 2014-11-24 14:32:59 -0600

crduggin

800 ●5 ●5

I have modeled indirect evaporative cooling in the VE before. My system had two stages of evaporative cooling on the exhaust side that then runs through a heat exchanger. I ended up having to model the evaporative cooling with cooling coils rather than the spray chamber component. The possible controlled variables for the spray chamber were too limited. I controlled the cooling coils via heat transfer using the value from the manufacturers materials for each stage. I used an 80% sensible effectiveness for the heat exchanger. The cooling coil controls staged on and off based on the supply side leaving DBT off the heat exchanger. I hope this helps even though it's a bit late.