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How to model service hot water for midrise apartments

asked 2016-05-31 12:42:20 -0500

Morteza gravatar image

What is the best way to model Service Hot Water for a MidriseApartment in OpenStudio? Assuming each apartment unit has its own water heater, is it more appropriate to select separate water use connections and water use equipments for each of the apartment units, which is very time consuming, or is it okay to select a water use connection for a group of the apartment units located in each floor or in the whole building?

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answered 2016-06-01 01:17:29 -0500

updated 2016-06-01 01:29:40 -0500

Adding a new plant loop with a water heater and a water use connection for each apartment would be a very easy task using a measure. But you'll get dinged on simulation time if you end up with 150 plant loops. Here is some pseudo code if that's helpful: Loop on all spaces, check if the spaceType corresponds to appartment, if so create a plant loop with the necessary components (water use connection and equipment, water heater, pump, setpoint manager). You can also get the spaceType you need and call spaceType.spaces...

Note that all of that can de done using or adapting some of the work done as part of openstudio-standards. See Prototype.HVAC_Systems.add_swh_loop and Prototype.HVAC_Systems.add_swh_end_uses especially.

I guess the true question is what do you know about the efficiency of the water heaters in each space? Are they modulating? Is it a tank-style water heater that just turns on and off? If natural gas, do you have an automatic damper to close the flue when the water heater is off (are standby losses a big factor?) Is water heating usage a big driver in your building? How well do you think you know the actual hot water draw versus various losses?

The answer to these questions will determine whether it's an appropriate assumption to model it as a single water heater or if it would be too crude of an assumption.

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(I realize this is in the gray area between a comment and an actual answer)

Julien Marrec gravatar image Julien Marrec  ( 2016-06-01 01:18:31 -0500 )edit

@Julien, thank you very much for the helpful information, I will study these options carefully. However, I did not find any measure for service water heater in BCL library, could you please provide a link to this measure? In addition, this is a LEED project and the baseline model should be consistent with ASHRAE 90.1-2007 modeling protocol, hence I have to provide answer to the entire question that you mentioned from the standard for the baseline model, is this correct? Thanks again for all your help!

Morteza gravatar image Morteza  ( 2016-06-01 11:04:11 -0500 )edit

If there's no mesure in BCL you have to create it. It'll be a simple mesure though.

Not sure I understand what's your actual question about the LEED and ASHRAE protocol

Julien Marrec gravatar image Julien Marrec  ( 2016-06-02 05:25:11 -0500 )edit

Julien, thank you for your response. I am not quite familiar with creating measures, so thought using following procedure to model SHW for the apartment units of the model: 1. Create a new plant loop with a water heater and water use connections 2. Select an unconditioned space in the underground parking garage that is not part of the building total floor area 3. Select a multiplier equal to the number of apartment units within the building for the Thermal Zone of the selected space. 4. Select this space as “Space Name” for each of the Water Use Equipments Is this procedure correct?

Morteza gravatar image Morteza  ( 2016-06-03 17:56:57 -0500 )edit

You actually don''t have to specify a space name in the water use equipment. This is optional, to account for heat gains (latent).

This would work if you only care about getting hot water heating consumption in your model, but keep in mind it's a simplification

Julien Marrec gravatar image Julien Marrec  ( 2016-06-04 03:36:59 -0500 )edit

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Asked: 2016-05-31 12:42:20 -0500

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Last updated: Jun 01 '16