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I agree that a single central plant isn't the best option if there are multiple individual DHW systems in the multifamily building. I would recommend molding each of the building's DHW systems as their own service hot water plant in OpenStudio. You don't need to model a separate service hot water loop for each apartment unless that's how the individual DHW systems in the building are configured. If that is the case, this post discusses using a measure to automate the process of assigning each water draw to its own service hot water loop and water heater, in case you want to investigate that approach or use that as a starting point for a measure that does something different.

The documentation isn't totally clear for how (or even IF) multipliers for a single zone or group of zones in EnergyPlus & OpenStudio affect service hot water draws. There are some closed issues on EnergyPlus Github from years ago here and here on this topic, so you may want to do some testing on the impact of zone multipliers on:

• the flow rate of hot water delivered
• heating gains for the zone(s) where the hot water draws are assigned
• heating gains for the zone(s) that contain the hot water heater

If the results from testing make sense, then I would recommend leveraging multipliers to speed up your workflow and represent identical zones. This means:

• zone internal gains (lighting, occupants, etc.) are identical (schedules and peak gain values)
• zone hot water draws are identical (schedules, peak flow rates, target temperatures)
• those hot water draws are on the demand side of a service hot water plant with identical supply equipment (i.e. hot water heaters). In other words, if one zone is served by a heat pump water heater and another zone served by a natural gas water heater, those zones should not be combined together with a multiplier of 2.

You can see how zone multipliers are used in the hospital commercial prototype.

I agree that a single central plant isn't the best option if there are multiple individual DHW systems in the multifamily building. I would recommend molding modeling each of the building's DHW systems as their own service hot water plant in OpenStudio. You don't need to model a separate service hot water loop for each apartment unless that's how the individual DHW systems in the building are configured. If that is the case, this post discusses using a measure to automate the process of assigning each water draw to its own service hot water loop and water heater, in case you want to investigate that approach or use that as a starting point for a measure that does something different.

The documentation isn't totally clear for how (or even IF) multipliers for a single zone or group of zones in EnergyPlus & OpenStudio affect service hot water draws. There are some closed issues on EnergyPlus Github from years ago here and here on this topic, so you may want to do some testing on the impact of zone multipliers on:

• the flow rate of hot water delivered
• heating gains for the zone(s) where the hot water draws are assigned
• heating gains for the zone(s) that contain the hot water heater

If the results from testing make sense, then I would recommend leveraging multipliers to speed up your workflow and represent identical zones. This means:

• zone internal gains (lighting, occupants, etc.) are identical (schedules and peak gain values)
• zone hot water draws are identical (schedules, peak flow rates, target temperatures)
• those hot water draws are on the demand side of a service hot water plant with identical supply equipment (i.e. hot water heaters). In other words, if one zone is served by a heat pump water heater and another zone served by a natural gas water heater, those zones should not be combined together with a multiplier of 2.

You can see how zone multipliers are used in the hospital commercial prototype. .