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Re: [EnergyPlus_Support] unable to reach set point temperatures in zones





Hi,

1. Unlike conventional Air based system, Radiant system is quite tricky to model and investigate. In my opinion, the sensible capacity is very important factor to consider in while studying Low Energy System performance. As per a research document from Berkeley it says that the slab integrated system could meet only 'sensible cooling capacity on the order of 24 Btu/hr-ft2 (~7 W/ft2 or 77 W/m2 )  active surface, not including associated ventilation systems or strategies'. So you need to look into the total heat load (sensible+Latent) for the space where Radiant system is being implemented. If the latent load is high enough then you might need to incorporate DOAS system in your design to handle Outdoor Load which brings most part of the latent load in the building apart from people and infiltration. Refer following link to explore more.


Source: http://www.cbe.berkeley.edu/research/pdf_files/IR_RadCoolScoping_2006.pdf

2. Condensation control for Radiant system is something must looked into as mentioned by Mr. Jean. Default setting in E+ is when any condensation happens the Active surface  will be turned off which might be one of the issue causing high zone temp in the model. 

3. Also check zone air temp, operative temp and Radiant temp to understand how radiant system is responding to the loads. In typical fully functional radiant system following behavior in air temperature could be realized. 

Inline image 1


Hope this helps!!

On Sun, Feb 11, 2018 at 2:43 AM, srk.iitm@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
 

Please see the below attached file of radiant cooling system served by a purchase cooling.

I designed as per Design Day conditons and I got the cooling load for set point temperature of 24 degC ....

Purchased cooling Design capacity: 14.876 kW
Flow rate: 0.001772 m3/sec

when I simulated for the same city, I am not getting temepratures equal to that of set point.

These are the peak temperatures that I am noticing:

west Zone: 30.9572 degC

east Zone: 31.1degC

North zone: 28.67 degC

peak cooling capacity of Purchased cooling observed in simulation reports is : 35.2613 which is way higher than the design capacity 14.876 kW. Why is this? the peak capacity should not be greater than the design one right?

peak cooling zone capacities are 

west zone: 12.414 kW
East zone: 11.331kW
North Zone: 12.707kW

where as the design capacities are 

west zone: 4.454 kW
East zone: 4.575kW
North Zone: 5.846 kW
Why is this? the peak capacity should not be greater than the design one right?

during what conditions I can see both the simualted peak capacity and design capacity same?


What should I do to pull down the temperatures to that of set points? eventhough it is not practical, I maintained the temperature of cooling water as 5 degC. I tried changing the capacity of purchased cooling. but it is limted to accept only upto certain capacities. beyond that it is not accepting...what should I do to pull down the temperatures?





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Javed Iqbal, LEED AP, CEA
Sr. Energy Analyst 







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Posted by: Javed Iqbal <eee.javed@xxxxxxxxx>


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