HVAC system settings

asked 2016-05-23 08:19:51 -0500

Wilson gravatar image

updated 2017-05-06 08:32:45 -0500

Hi! I'm using OpenStudio to model my building. I don't have experience in HVAC systems design and my doubt is related with it. When I started my OS project I added one HVAC template(Packaged Rooftop heat pump) and I didn´t make any HVAC changes. image description

In a summer week simulation, when the outside temperature is above about 35 celsius degrees the interior temperature is out of the cooling setpoint limit. (Picture)image description

A few weeks ago I made a question related with a cooling problem and it was answered me that I was controlling the cooling coil using the SetpointManager:SingleZone:Reheat object and to solve this I have to add another SPM to control the cooling coil using SetpointManager:SingleZone:Cooling. Can this problem be related with it? I'm trying to find in the HVAC library SPM that can help me with this problem but with no success. Can you please give me your opinion about how can I solve this problem? Thank you

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This looks like a sizing issue...

Is your system autosized? Are you using the right design days to match your weather file?

Julien Marrec gravatar image Julien Marrec  ( 2016-05-23 08:49:19 -0500 )edit

Thank you for your answer Julien Marrec. Yes, the system is autosized. The *.epw that I'm using was made from my measured data(I only have temperature information) and I'm using the *.ddy provided by E+ website for the nearest area(10Km distance). I'm running just 1 week simulation. If the system is autosized I have to create my *.ddy file? In case of hardsized is the *.ddy needed? Thank you

Wilson gravatar image Wilson  ( 2016-05-23 09:08:12 -0500 )edit

It could be that your measured data has days that are worse than the design days. Try modifying sizing factors for now, put something like 3 instead of 1.15 or 1.25, and see if you still have the same problem. If not, then your design days can be the problems

Julien Marrec gravatar image Julien Marrec  ( 2016-05-23 09:34:35 -0500 )edit

I changed the Sizing Factor to 3 and it reduced the unmet load hours(16 to 5). What you advise? Create my *.ddy file? I just have measured data for temperature. Thank you

Wilson gravatar image Wilson  ( 2016-05-23 10:37:12 -0500 )edit

5 hours out of 8760 unmet is not a problem IMO. It looks like you are not cooling on 07/17. Check the schedules (HVAC electricity may not be the whole story). Is the zone actually trying to do cooling on that day? Is it a Sunday ? The problem on the day after can be fixed by turning on cooling earlier and ramping the temperature set point. It can't respond instantly. That room is still hot from the day before. I think your system is fine. Its your schedules you should check.

TomB gravatar image TomB  ( 2016-05-24 20:09:49 -0500 )edit