Uncontrolled heat gains

RE: Uncontrolled heat gains

Stephen Brown — Thu, 18 Feb 2016 15:30:41 GMT

Hi Jose,

My apologies. I have checked this further and found my first post to be incorrect. DDB Summer calculates the peak summer operative (Resultant) temperature as per CIBSE Guide A. Please disregard my previous comments.

Best Regards
Steve

RE: Uncontrolled heat gains

José Alberto Gil Machín — Thu, 18 Feb 2016 12:08:37 GMT

Hi Steve,
May I´m wrong but I think the Resultant temp. is the worst case, as we are going to have a heating effect instead of a cooling effect in summer due to the wall temperature. As with the Heat Gains the Resultant temp. would be more conservative, to evaluate the overheating in summer, I think the same Resultant temp. will be higher than the Air temp. If I´m wrong with this line of reasoning, please let me know.
Regards,
Jose

RE: Uncontrolled heat gains

Stephen Brown — Thu, 18 Feb 2016 11:54:03 GMT

Hi Jose,

The two calcs are doing different things. Gain is calculating the cooling load required to achieve a specific a design temperature (Air or Resultant). Resultant is often used for this calc to achieve comfort conditions. Summer is predicting the air temp in the absence of any cooling and therefore the cooling effect on surfaces etc does not come into play. The Air temp would be the worst case and as such is a better predictor of if mechanical cooling is required for a room.

Best Regards
Steve

RE: Uncontrolled heat gains

José Alberto Gil Machín — Wed, 17 Feb 2016 15:26:02 GMT

Hello Steve,

Thanks for your quick response.

I think the software should have the option of using the Resultant temp. for the Summer calc. because there´s an important different results when you do the Heat Gains calcs. using the "Air" temp or "Resultant" temp., which is normal. I do appreciate your comments.

Regards,

Jose

RE: Uncontrolled heat gains

Stephen Brown — Wed, 17 Feb 2016 13:26:30 GMT

Hello,

Please post your second question regarding CIBSE Heat Gain to a separate thread and I will try to answer it there.

With regard your question on Summer - The Summer calc uses Operative Temp as defined in CIBSE Guide A5 Section 1.2.2. This equates to Air temperature for the purposes of our calc and comfort conditions.

There is scope in CIBSE to calculate Resultant Temp but the conditions for this are where there is less than 0.4degC between the Operative Temp and Mean Radiant Temp. As such there would be very little difference between an Air or Resultant Temp as Resultant Temp is made up of 1/2 Air and 1/2 Mean Radiant Therefore we do not consider Resultant Temperature for the Summer calc.

Hope that helps.

Regards

Steve

RE: Uncontrolled heat gains

José Alberto Gil Machín — Tue, 16 Feb 2016 17:12:03 GMT

Hello again Duncan:
Regarding the Summer temperature calculation, I think the software gives the air temperature instead of the resultant temperature. If I am correct, is it possible to obtain the resultant temperature using the Summer calculation?
Another question a bit different: when I do the Cibse Heat Gain calculation, why do I have different gains from the casual loads if I use the air temperature than when I use the resultant temperature? (If I have to create a new question regarding the last question, please let me know)

RE: Uncontrolled heat gains

Duncan Brown — Wed, 11 Mar 2015 15:44:55 GMT

Sarah

I think you should be considering the Summer calculation.

Regards,
Duncan