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Forum discussion

NC-2009 EAp2:Minimum Energy Performance

Hotel System 2 Reheat

I am currently modeling a hotel with less than 20,000sqft (specifically 19720) of non-residential space. When modeling I understand I must use system 2 (as it has electric heating) for the baseline system. These coils are built in the pre-heat configuration. I have humidity sensors in multiple zones in the non-residential spaces, as such I have inputted a humidity control sensor in the baseline system per ashrae for those areas. This leads me to overcooling the space and causing unmet hours, because in the baseline system it is impossible to reheat the air since the heating coils are in the pre-heat orientation. At this point, do I add electric resistance heating coils into the baseline system in reheat position? I can't just move the heating coil, as a heat pump is impossible to simultaniously heat and cool with that system alone. Use a narrative? Thank you for any assistance.

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Profile picture for user Marais.Jean
Jean Marais
b.i.g. Bechtold DesignBuilder Expert
LEEDuser Basic Member
581 thumbs up

Tue, 10/08/2013 - 13:54

Ha. I bet you get HPs that can both heat and cool at the same time. In essance two units sold as one...it would be interesting to see if you could order equipment like this, i.e. PZHP with dehumidification function. What software are you using? Would it make sence to add an extra HP for the reheat function (the system 2 doesn't mention electirc resistance heating)?

Tue, 10/08/2013 - 14:09

I don't know if your situation is different, but I had to model a building where the humidity control was necessary to avoid condensation on the floors, which were cooled by chilled water. Therefore I considered the humidity control and the cooled floor as part of the same system. Since in the baseline model there was no cooled floor, in the baseline model I modeled no humidity control. Regards

Tue, 10/08/2013 - 14:20

The modeling software is IES Virtual Environment Pro, I could in fact model a system with a heat pump as a re-heater, it just didn't seem realistic and I didn't know if that was what I should do.
Profile picture for user Marais.Jean
Jean Marais
b.i.g. Bechtold DesignBuilder Expert
LEEDuser Basic Member
581 thumbs up

Tue, 10/08/2013 - 16:07

1) User Manual: G3.1.3.1 electric heat pumps used for baseline building systems 2 & 4 shall be modeled with electric auxiliary heat...so you have the heat pump + an auxilary heater for temps below 40ºF, i.e. electric resistance (my bad). So you could use an electric resistance heater to reheat. That being said, I did not find where the standard says that dehumidification is required for the baseline if it is in the proposed, but as all setpoints (including humidity setpoints) should be the same for both, it is implied. 2) User Manual:G3.1.2.7 the drybulb high-limit economizers may increase energy use in dry or cold climates when spaces are humidified. This does not preclude modeling the baseline system with that humidification and economizer...I take this to mean that humidification is a process load to be modelled the same in both baseline and designcase models.

Tue, 10/08/2013 - 17:20

It sounds like electric resistance heat should not be used to reheat, as the temp isn't below 40 degrees. This is in Florida, so economizers are not used. Also Should I change the coil positioning from pre-heat to re-heat in the baseline, assuming I am able to reheat using electric heat? is that even allowed?
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Wed, 10/09/2013 - 20:43

This is a good one without a clear answer. You could try to model the same reheat configuration in the baseline as is in the proposed case. This keeps it cost neutral. You could try to explain to the reviewer the issues that cropped up when you did not have the reheat system in the baseline. Maybe even show the reviewer the results without reheat. In other words provide a good, thorough explanation. Alternatively you could submit a LEED Interpretation and ask USGBC what you should do.

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