Tank less DWH

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Hello, everyone

I am trying to model a new DWH (Intelli-hot system Gen-II-iQ1501) for a
mid-rise residential building. This is a high-output, on-demand water
heater, which eliminates storage tank, standby losses, and mixing valves.
Per the manufacturers and the project?s engineer notes, expected savings on
hot water for this type of WH compare to a regular storage tank WH is 30%
to 40%. I am wondering what type of WH should I select for the Baseline
Case in order to comply with ASHRAE/LEED energy modeling protocol.

Your thoughts and suggestions would be highly appreciated,

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

I don?t believe I?ve ever documented 30-40% Service Hot Water savings on unitary heating equipment alone. Either your designer/manufacturer must also be counting on serious reductions with low flow fixtures, or somebody is trying to sell something...

The Appendix G Table G3.1 will direct you back towards the table at the end of the Service Water Heating section in 90.1 for direct guidance on what the baseline case should reflect in relation to your proposed case instantaneous heaters. Looks like for your make/model you?ll be needing to address both thermal combustion efficiency AND determine standby losses based upon the capacity of the unit cited.

I?d advise caution before immediately entering ?n/a? for proposed case standby losses in your LEED documentation. Consider whether in fact there is a storage tank somewhere, or other opportunities outside of combustion and piping distributions for heat to leave the system.

For the proposed case side, I might poke the manufacturer (time allowing) to provide you a thermal efficiency (combustion + condensate recovery) at a sampling of firing rates for a given delta (ground water --> delivery temp), and use that data to evaluate whether the library curves eQUEST assigns for instantaneous gas boilers is in alignment or otherwise needs tweaking. If you don?t have time to dive this far I?d simply be mindful to ensure baseline + proposed case curves are at least matching.

Hope that helps!


[cid:image001.png at 01D2E912.F83239D0]
Nick Caton, P.E., BEMP
Senior Energy Engineer
Regional Energy Engineering Manager
Energy and Sustainability Services
Schneider Electric

D 913.564.6361
M 785.410.3317
F 913.564.6380
E nicholas.caton at schneider-electric.com

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

[cid:image002.png at 01D2E912.F83239D0]

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400


Thank you for your guidance, as always your suggestions is very helpful.

I am agreeing with you that serious energy savings related to service hot
water serving is through low flow fixtures, however the manufacturer
provided some engineering data, including thermal efficiency, of the water
heater (page 8 of the attach file) that I thought can be helpful to achieve
more savings.

I wanted to be sure on selecting the correct system for the base model. As
I understand from your suggestions, since this is storage less heater in
the proposed design, for the baseline model, I have to select ?Gas
instantaneous water heater? in Table 7.8 and there are no any other
options, is this correct?

I truly appreciate your help,

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

I think there are two separate issues. The vendor is comparing their system as a retrofit to an older and inefficient system. For Appendix G modeling purposes you wouldn?t compare against that existing hot water system, the baseline would be the code minimum new system as selected by your building?s characteristics.

So even if the system did save 30% to 40% against existing storage systems, it won?t likely do that against an Appendix G baseline.

Arriving at the 30% to 40% figure for existing building retrofits is a whole different can of worms ? tank losses could be reduced for sure. The thermal efficiency is shown to be very high. There are many other losses in the existing system that may also come into play though, so the rule of thumb savings figure is difficult without saying ?percentage of what? ? it wouldn?t affect the flow rates as you mention which is an additional opportunity, and if the system is recirculating it will have losses from that activity.

Looks like a good product though, definitely some energy reduction potential for sites that fit the capacity and venting requirements.


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

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