Re: [EnergyPlus_Support] Internal Loads

[Philip Haves <phaves@xxxxxxx>]

Peter,

I expect your 'problem' comes from the fact that your internal gains are 
all radiative but you are (presumably) controlling the air temperature.  
When the radiant internal gains are present, they will be absorbed at 
the interior surfaces of the space, increasing the surface temperature 
above what it would be in their absence but with the same air 
temperature.  The increased surface temperature produces greater 
conductive heat loss through the envelope.  This probably explains what 
you are seeing.  Try the experiment again with purely convective 
internal gains - the change in load should then equal the magnitude of 
the change in the internal gains.

Phil

Wilde, Pieter de wrote:

>Dear list-members,
>
>I have a question about internal gains. I am currently running a simple building (1 zone) under the climate of Stockholm. Internal gains are modeled as "other equipment", 300 Watt, 100% radiant. The schedule for this equipment is "on"  all the time. I want to calculate heating loads, using the Purchased Air System. What is puzzling me is the following:
>
>If I run the file I can see the heating is working all the time in January, February etc as the indoor temperature is constantly my setpoint value of 20 degrees Celcius, and the heating energy is pretty constant. Now if I turn OFF my internal loads by reducing the 300 Watt to 0 Watt, I would expect the heating energy per timestep to increase with 300 W x 3600 = 1080.000 J. However, the difference between heating energy with and without internal load is only about 930.000 J. No other mods were made between these two runs. In the file without internal loads the temperature is 20 degrees as well, so all internal gains should contribute to the heating.
>
>Does anybody have a pointer to what might be causing this? May-be something in the Purchased Air approach, or???
>
>Thanks for any advice!
>
>Best regards,
>
>Pieter de Wilde
>
>
>
>P.J.C.J. (Pieter) de Wilde
>TNO Building and Construction Research
>Email:  P.deWilde@xxxxxxxxxxx
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-- 
Philip Haves
Leader, Commercial Building Systems Group
Lawrence Berkeley National Laboratory, MS 90-3111
Berkeley, CA 94720
Tel: (510) 486 6512
Fax: (510) 486 4089






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