System fans

rashmi sonal · Posts: 7

Hi Andy,

I modeled a building twice in Los Angeles. First with a VAV unit with terminal reheat and then with Hot water radiator with natural vetilation. For both the cases I had set the air distribution at minimum required per zone. The system fan loads for the VAV case is around .93 KW per hour and for the hot water radiator case I am getting 2.3 KW per hour. I just dont understand why the fan loads are more than double for hot water radiator case (all other parametsr being the same)

Thank you.

Regards
Sonal

Andy Tindale · Posts: 1196 Location: Stroud

Hi Sonal,

Assuming that you're using the same size fans in all cases, I suspect that the reason you have less fan consumption when using a VAV system is that you have the VAV 'supply air minimum flow fraction' set to a number less than one - the default is 0.3. Try setting this to 1 and you will probably get the same fan energy consumption as for the other systems. I guess this is partly what VAV systems are all about!

You can get some more information about how this works in DesignBuilder from the on-line help - search for 'air distribution'.

Regards
Andy

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