Re: [EnergyPlus_Support] RE: DX coil problem

Thanks Richard for your feedback.

The DX coil has been autosized that is why I surprised. However, as you suggested, I increased the DX cooling coil temperature up to 18C. However, the unmet hours increased too. My question is that:

1- Why DX coil does not work with full capacity, even I autosized it?

2- Is there any optimum setpoint temperature that I need to play to satisfy the unmet hours? I personally do not think that it helps. I think it might be that when the outdoor air temperature mixes with the current flow in the system, it might disturb the cooling coil capacity calculation? I also changed the cooling coil curves with different types, and it did not solve my problem.

3- Is there any other suggestion?

Thanks you for taking your time to answer my questions.

Best regards,

Eshagh

From: Richard Raustad <RRaustad@xxxxxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Wednesday, May 23, 2012 12:27 PM
Subject: Re: [EnergyPlus_Support] RE: DX coil problem

Is the DX coil autosized, or did you fix the capacity?

Coil:Cooling:DX:SingleSpeed,
    Zone1WindACDXCoil,       !- Name
    CoolingCoilAvailSched,   !- Availability Schedule Name
    autosize,                !- Rated Total Cooling Capacity {W}
    autosize,                !- Rated Sensible Heat Ratio
    3.0,                     !- Rated COP {W/W}
    autosize,                !- Rated Air Flow Rate {m3/s}

Did you check your sizing inputs? Try raising the Zone:Sizing object cooling supply air temp, this will increase the zone flow rate and possibly give you more DX cooling coil capacity.

On 5/23/2012 12:20 PM, Eshagh wrote:

Hi,

I would be happy if someone helps me with the following issue.

I use system 6 for my baseline simulation in weather 1b which is hot climate . The AHU consists of Outdoor air mixer, variable fan, electric heating coil and DX cooling coil. I ran the simulation and the flow rates are fine (the OA and maximum flow rate). However, I have problem with the DX coil. I think the coil can not cool down air temperature enough to satisfy my set point temperature that is 14C. The profile before and after cooling coil has about 14-15C temperature difference with a special pattern. The temperature should be constant (14C) but it cools down and keeps it pattern like before the cooling coil. I just noticed that when I turn off the out door air (OA), the temperature becomes constant (14C) and it's fine. However when I add the outdoor air flow rate (about 46C in July) again, the cooling coil cools down but as I mentioned, again it does not cool down to 14C. Could anyone please let me know what else I can check for solving this problem? Can the cooling curves cause the problem?

Thanks,

Eshagh

-- 
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
1679 Clearlake Road
Cocoa, FL  32922-5703
Phone:   (321) 638-1454
Fax:     (321) 638-1439 or 1010
Visit our web site at: http://www.fsec.ucf.edu

UCF - From Promise to Prominence: Celebrating 40 Years