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Forcing an upgrade to have zero unmet hours

asked 2020-03-07 17:17:27 -0500

y.tanaka gravatar image

Using PAT Tool v.2.8.0 with ResStock's project_singlefamilydetached to run analyses.

Was wondering if there's a way to force PAT tool to create an end-use load profile where there are zero unmet hours? I'm currently using the ASHP, SEER 16, 9.0 HSPF upgrade option on a building stock that's fixed in a IECC Climate Zone 6 area. There are some buildings that will have up to 30% of the year having hours that do not meet the heating setpoint temperature. During some of these hours, the zone air temperature and the zone thermostat temperature will differ by up to 10° F.

My objective is to run PAT tool with any HVAC system and observe the end-use load profile on the basis that it can meet heating load 100% of the time out of the year.

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It's probably impossible to have zero unmet hours due to factors such as basements, thermostat setpoint schedules, season assumptions, and the Manual J/S sizing algorithm in general. Oversized electric baseboards are best suited to getting zero unmet hours since they can heat conditioned basements with independent thermostats, as opposed to heating them as a slave zone.

Are you seeing substantially more unmet hours after the upgrade compared with before?

Eric Wilson gravatar imageEric Wilson ( 2020-04-08 11:18:14 -0500 )edit

The following is the OS result for an Electric Baseboard upgrade without the oversizing:

Time Setpoint Not MetTime (hr) During Heating 45.33 During Cooling 58.33 During Occupied Heating 45.33 During Occupied Cooling 58.33

The following is the OS result for Electric Baseboard upgrade with the all coils oversized by 150%:

Time Setpoint Not MetTime (hr) During Heating 45.0 During Cooling 0.0 During Occupied Heating 45.0 During Occupied Cooling 0.0

The above is for one building.

y.tanaka gravatar imagey.tanaka ( 2020-04-12 14:16:16 -0500 )edit

45.33/8760 = ~0.5%. I believe Manual J/S dictates that design day conditions exceed 99% of annual hours, so 0.5% seems totally reasonable to me.

Eric Wilson gravatar imageEric Wilson ( 2020-04-13 08:44:51 -0500 )edit

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answered 2020-04-13 08:45:55 -0500

It's probably impossible to have zero unmet hours due to factors such as basements, thermostat setpoint schedules, season assumptions, and the Manual J/S sizing algorithm in general. 45.33 unmet heating hours out of 8760 = ~0.5%. I believe Manual J/S dictates that design day conditions exceed 99% of annual hours, so 0.5% seems totally reasonable to me.

Oversized electric baseboards are best suited to getting zero unmet hours since they can heat conditioned basements with independent thermostats, as opposed to heating them as a slave zone.

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Asked: 2020-03-07 17:17:27 -0500

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Last updated: Apr 13