[Bldg-sim] Multi-Family DHW

David Eldridge via Bldg-sim bldg-sim at lists.onebuilding.org
Fri Dec 9 10:05:15 PST 2016

Designers and modelers run into this all the time – putting Appendix G aside for now, there is a real impact to the operating cost of the building, and also the site/source energy use, and also the construction cost of the building.

The developer may be thinking about other factors though, such as how the energy will be metered to the units when the facility is occupied, or they may prefer for the units to have their own water heater instead of a central system, if natural gas was used to do this where to run natural gas lines, where to put the flues, etc. and construction cost for that would likely be higher.

Anyway, you’ll have to run the numbers in the simulation to see whether the net impact is large or not relative to your other energy efficiency measures, and identify any trade-offs that need to be made to offset the energy costs. The potential is there for it to be a step backwards for Appendix G performance.

There are a few variables that can make the impact larger or smaller in the design of the DHW system as well. You mentioned high-efficiency water heater units. Hopefully the facility is also using low-flow fixtures to reduce the total DHW quantity consumed, which should reduce the impact for using electricity as the fuel in the proposed case.


David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates

From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Sunayana Jain via Bldg-sim
Sent: Friday, December 09, 2016 11:36 AM
To: Angelica Walsh via Bldg-sim <bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] Multi-Family DHW


We are working on an energy model of a high-rise multi-family building in the New Jersey climate zone. This project will be using high efficiency in-unit electric water heaters (0.95 EF) for DHW requirements.

As per the latest code (ASHRAE 90.1-2013 Appendix G), baseline DHW system for a multi-family building has to be a gas storage water heater. As I understand, there will be a significant energy cost penalty for using electric fuel versus natural gas in the design for DHW.

Has anyone encountered similar situation?


Sunayana Jain CEM, LEED AP BD+C
Sustainable Buildings & Operations Project Manager
Sustainable Solutions Corporation

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