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[EnergyPlus_Support] Re: DX coil problem

Richard said to raise the supply air temp in the zone sizing object. Doing this tells e+ that the incoming air will carry less cooling so you'll need more of it to balance the loads. So the coil dx unit will be specified (auto sized) for a higher air throughput. Then when the actual air throughput is less, then it is sort of oversized and can reach the required output air temp.  Baseline supply air temperature requirement should be (RoomsetpointT - 11 deg C, I think) so for a room cooling setpoint of 24 this is 13 deg C. So you will need to set that up, probably with SetpointManagers.

 



--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Eshagh <isac_moh@...> wrote:
>
> 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@...>
> 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
>




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