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NC-2009 EAp2:Minimum Energy Performance

Hotel occupancy rate and a/c energy consumption

We have a hotel project with VRF systems serving the guest rooms. I am struggling with coming up with a way to simulate less than 100% occupancy rate in the hotel guest rooms. I am using HAP and all zones in the terminal system use the same schedule and they all can be either ON or OFF at the same time. A the moment I have all of the rooms ON/occupied mode/ all of the time and the VRF systems see all of the connected terminal zone units as 100% of the time in occupied mode. We have automatic door key interlock to turn off the a/c units when the room is not occupied and I don't find a way to simulate certain percentage of the rooms being in unoccupied mode. There are quite a few studies indicating that hotels typically have no more than 70 to 80 % occupancy rate. For this project it is especially important to simulate less than 100% occupancy rate because the VRF system has good efficiency in partial load. Would it be acceptable if I leave the thermostat schedule ON/occupied mode/ all the time and simulate the system efficiency as IEER which I understan is similar to the IPLV and NPLV for chilles? Should we present it as exceptional calculation method or narrative would be enough?

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Wed, 02/22/2012 - 13:56

Does HAP even accept an IEER? This is a question for the developers/users of HAP. Try the HAP discussion group at onebuilding.org. Since HAP does not model these systems directly you will need to find an acceptable, published work around to use in order to model them at all. Not sure why you can't change the schedules to accommodate the less than 100% occupancy. Every modeling software should be able to do this as far as I know. If you find a work around it should be submitted as an exceptional calculation.

Wed, 02/22/2012 - 15:44

Marcus, thanks for your prompt reply! HAP does not really accept IEER. I was thinking to use it as a EER since my system is on all the time and really don't find any other way to simulate that some of the rooms are in unoccupied mode, fan off. I understand it is a stretch but I don't find any other way of simulating part load performance to account for 20 to 30% of the connected rooms in unoccupied mode (fan coil fan OFF) therefore VRF condensing unit is in 70 to 80% loading even in worst outdoor and internal load conditions. I have a model that has the VRF system simulated as chilled water and probably will present it like this. With respect to the schedule question, i do have occupancy schedule that varies the number of people during the day but what I don't find is how to simulate thermostat/fan schedule. There is only ON or OFF and in HAP ( as well in eQuest and Visual DOE) it is applied across all connected zones, thus all rooms are either ON or OFF at certain hours of the day. The issue even with the chilled water simulation is that I have basically all the toms in occupied mode all the time and do not simulate a real time hotel occupancy rate of 70 to 90% where rearly all rooms are booked and occupied at the same time. Thanks again for your help!
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Wed, 02/22/2012 - 16:29

Modeling a VRF as chilled water does not make much sense to me. The published workaround we use in eQUEST models these systems as heat pumps. The limitation is this does not account for any simultaneous heating and cooling. Not sure how to help you with the zoning and schedule modeling issue in HAP. I would recommend you contact the HAP folks or the HAP users group at onebuilding.org.

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