[Equest-users] an inadequate cooling capability warning

[Bruce Easterbrook]

     I think your control strategy is not right or you are 
misinterpreting how equest works.  You say your room requires cooling at 
all times of the year and you want to keep your maximum temperature 
below 104F.  You have selected 90F as your control point which is the 
setting of your room t-stat.  Your 55F temperature only matters if you 
have potentially freezing temperatures in the winter because you have a 
water coil which you don't want to freeze.  Below 55 your economizer is 
shut off and you should be on minimum fresh air which with no personnel 
in the pump room should be at .06 cfm/SF, you will be almost at 100% 
return air.  You should have a differential temperature or enthalpy 
controller to control the economizer.  Your system will remain like 
this, considering std equest defaults until the room temperature reaches 
92 F.  If the outside air temperature is above 55 the system will use 
the economizer to control the temperature.  If that fails it will use 
the cooling coil.  You don't want both the economizer and the cooling 
cool running at the same time.  Basically you don't want to use water 
pumping energy if you don't have to as it is additional energy on top of 
the fan.  Practically you could have 2 temperature controllers 
controlling part of the same air stream and the system will hunt.  The 
only other variable here is the water temperature in the summer.  
Basically your peak heat generation in the pump room and your peak water 
temperature in the summer will set your system CFM, coil size, coil 
flow, pump size.  This is a basic explanation, there are more things to 
play with to fine tune the system further.
Bruce Easterbrook P.Eng.
Abode Engineering

On 02/08/2010 03:09 PM, Kevin Kyte wrote:
>
> I have been struggling with this scenario.  A pump room does not need 
> to exceed 104F. Lake water is used for cooling.  The room is expected 
> to contain internal loads requiring cooling at almost all times.  
> Below 55F the OA and RA modulate to provide 55F supply air.  Above 
> 55F, 100% OA and the cooling coil turns on.  I have the cooling Tstat 
> set to 90F and cooling coil available at 55F.  I am unsure how to even 
> model Below 55F except for economizing which is not really exact but 
> when I set the economizing low limit to 55F I get 200F in the space.  
> I have set economizing to 90F integrated with the coil and no low 
> limit.  The cooling coil is rarely used and not needed in its full 
> capacity yet I am getting inadequate cooling warnings.
>
> The Min-Supply-T is set to 55F because supply should not be less than 
> this and hourly reports show acceptable supply temperatures into the 
> mid 70s (I don't know if this is acceptable to the program?)  I am not 
> using a lake water chiller because I am not trying to use the same 
> coil temperature.  I am using a simple packaged single zone with the 
> cool-control range set to max and EIR zero'd because there is enough 
> force off the main header to not need any pumping through the loop.
>
> This is only for energy code compliance and I need an explanation on 
> the warnings.  Other than stating several obvious limitations I don't 
> really understand why this warning is occurring.  Does anyone have 
> suggestions on how I may model this system?
>
> I understand that electronic files would help and I will work on that.
>
> Thank you.
>
> Kevin Kyte, LEED^ ^® AP
>
> *Watts** Architecture & Engineering, P.C.*
>
> 95 Perry Street, Suite 300
>
> Buffalo, NY 14203
>
> p:  716.206.5174
>
> f.:  716.206.5199
>
> e: kkyte at watts-ae.com <mailto:kkyte at watts-ae.com>
>
> http://www.watts-ae.com <http://www.watts-ae.com/>
>
>
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