Forcing an upgrade to have zero unmet hours

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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y.tanaka

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

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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 (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 Met Time (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 Met Time (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 (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 (2020-04-13 08:44:51 -0500) edit

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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. 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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Eric Wilson

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

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You can force a constant zone temperature in ResStock v2.2.4 models by using the measure Ideal Air Loads Zone HVAC. There are some additional edits you need to make to the osm in order to implement Ideal Air Loads Zone HVAC, including deleting Energy Management System (EMS) objects and rewriting ResStock's default heating and cooling setpoints. These are legacy objects from the existing HVAC system in the IDF that the Ideal Air Loads Zone HVAC measure removes. If the simulation is run with EMS objects and Ideal Air Loads objects in the same IDF, it will fail.

The Ideal Air Loads Zone HVAC measure "will replace the existing HVAC system with ideal air loads objects for each conditioned zone." It can be found and downloaded here: https://bcl.nrel.gov/node/84744

I created a measure Clean_ResStock_for_Ideal_Air_Loads that, if placed before the Ideal Air Loads Zone HVAC measure in PAT, allows Ideal Air Loads to work with the ResStock workflow. Please contact me at sashadf@postroadfoundation.org if you would like to see it.