[Bldg-sim] [External] Multi-Family DHW

Maria Karpman via Bldg-sim bldg-sim at lists.onebuilding.org
Sun Dec 11 07:46:07 PST 2016

 I agree with David that in-unit electric heaters are often specified due
to low first cost, and to shift the burden of paying for water heating to
tenants. This also allows lowering the rent (not necessarily by the
sufficient margin), making apartments more marketable. Interestingly, the
Federal Trade Commission requires EnergyGuide labels for a wide range of
appliance (e.g. to show that a given TV may cost $15 a year in electricity
bills), but there is no such requirement for apartments, even though
difference in annual utility costs paid by renters can be $1,000+. So there
is no easy way for tenants to do apples to apples comparison of options
when shopping for an apartment, such as Annual$=12*Montly_Rent +
Annual_Utility_Costs. I think it is safe to assume that a label like that
will not be developed on the federal level in the next four years,
but there were some initial discussions about it in NY, and there is a tool
used in CA for low income tenants called California Utility Allowance
Calculator (CUAC). The technical side does not seem too complicated - it
could be an asset-style label showing anticipated energy cost paid by
tenants, including typical appliances/lighting, HVAC and DHW.

The incentive program in NJ allows either 90.1 2013 Appendix G w/addendum
BM package
or ASHRAE bEQ As-Designed
<http://www.buildingenergyquotient.org/asdesigned.html> path, and has no
rules against fuel switching. With App G path, a central gas storage water
heater is modeled in the baseline for multifamily projects irrespective of
the DHW fuel in the proposed design (Table G3.1, #11 (a) and Table

I agree with Fred that DHW distribution losses do not seem to be covered in
App G, and that there should be some related savings with in-unit heaters
versus central system. One challenge with using exceptional calculations
for that is to come up with a design for the central baseline distribution
– e.g. pipe length, sizes, location, etc. It seems that the intent of App G
was to prescribe DHW heating fuel and system efficiency, and that G3.1.3.6
should be expanded to include DHW. There seems to be no logical reason for
treating space conditioning piping losses differently compared to DHW
piping losses.

I am not convinced that distribution losses in *new* buildings meeting 90.1
2013 are significant given insulation and control requirements in Section
7. Quoting the NREL’s study in Fred's email, “…the range of distribution
loss varied widely (5%–61% due to loop configuration and operational
differences”. So even with the exceptional calculations, I’d expect a
sizable penalty from electric resistance water heaters. As David pointed
out, this penalty may be reduced by specifying low flow fixtures, and
also drain
water heat recovery
<http://energy.gov/energysaver/drain-water-heat-recovery>, solar DHW
pre-heat, etc. The program in NJ has incentives up to $1.7/SF, which is
hopefully enough to get developers interested in looking at measures that
affect tenant bills.


*Maria Karpman *LEED AP, BEMP, CEM


Karpman Consulting


Phone 860.430.1909

41C New London Turnpike

Glastonbury, CT 06033

On Fri, Dec 9, 2016 at 3:11 PM, Porter, Frederick NOR via Bldg-sim <
bldg-sim at lists.onebuilding.org> wrote:

> Interesting! First, Sunayana, are you sure you should be using *2013* App
> G/PRM? Even if the local energy code specifies ASHRAE 2013, LEED v4 uses
> ASHRAE 90.1-2010. And if utility programs are involved, there is usually
> some restriction on fuel switching. But that’s just bureaucratic detail.
> For the purposes of actually determining operating costs of *realistic*
> alternative systems, it’s not clear the standard (or most BEM software) is
> addressing this adequately. In larger multi-unit buildings, it is probably
> *not* practical to duplicate your proposed electric DHW system (in-unit,
> tank or instant), using gas, because all these heaters would require
> multiple flues, etc.  So a REAL alternative is a central DHW heater with
> recirculation.  That recirculation typically has considerable loop losses,
> which the PRM *seems* to have directed us to ignore. However if you read
> the text carefully, this restriction (G3.1.3.6) targets circulating fluids
> used for space conditioning.
> (“G3.1.3.6 Piping Losses (*Systems 1, 5, 7, 8, and 11*). Piping losses
> shall not be modeled in either the proposed or baseline building designs
> for hot-water, chilled-water, or steam piping.”)
> However, the DHW language seems ambiguous on this point. In any case,
> central DHW loop losses are sometimes close to the actual DHW use energy.
> So the real cost penalty of gas vs. electric may not be as large as it
> appears from a simple ratio of utility cost/Btu. California’s T24
> compliance software, though based on E+, has developed a much more rigorous
> approach to DHW calculations that at least considers piping losses in
> multi-family residential applications, along with researched draw profiles.
> The program passes off the DHW energy calculations to CSE (California
> Simulation Engine) for multi-family residential DHW.  Perhaps more
> accessible, a recent paper “Strategy Guideline: Proper Water Heater
> Selection” (http://www.nrel.gov/docs/fy15osti/63880.pdf) includes a
> broken link to MultiFamily_Central_DHW_EvaluationTool_v1.0.xlsx. You
> might try contacting the authors or Bldg America to see if you could get a
> copy. Output illustrated in the report is pasted below.
> If the project really can’t take the energy cost penalty caused by
> electric vs. gas DHW, and if the space heating uses HW boilers, there are
> systems that combine the DHW and HW piping; essentially the HW coils are
> supplied with potable water. This reduces the cost of piping and boilers in
> the building compared with separate DHW and HW. It does seem to penalize
> the efficiency of the heating side a bit, as the “HW” return temperature is
> often not as low as it would be for HW only.
> A related item for all to consider is that new gas tank type condensing
> DHW heaters are being rated at efficiencies of up to 99%. However, this is
> at a test condition which is rarely duplicated in reality (large flows of
> 60F inlet water). In any recirculating DHW system, the inlet T is usually
> much warmer, and in other cases, the draws are smaller and intermittent.
> Particularly the former reduces efficiency. That effect is considered in eQ
> and E+ models of HEATING condensing boilers, but not in the eQ DHW heater
> representation. So just plopping 1.01 into the “HIR” field of an eQ DHW
> heater is not realistic. (I’m not sure if E+ could be set up to represent
> this correctly or not.)
> I think there is some fodder here for LEED CIRs, ASHRAE Interpretations,
> proposed changes to the PRM, or direct questions to a code official or
> utility program manager. In addition to the never-ending battle to have
> simulation software that provides reasonable representations of building
> components and operation!
> Good Luck,
> Fred
> *Fred Porter, BEMP, LEED**©** AP*
> Principal Engineer
> Sustainability Services
> www.noresco.com
> *From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On
> Behalf Of *Sunayana Jain via Bldg-sim
> *Sent:* Friday, December 09, 2016 10:36 AM
> *To:* Angelica Walsh via Bldg-sim
> *Subject:* [External] [Bldg-sim] Multi-Family DHW
> All,
> 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?
> Thanks,
> *Sunayana Jain CEM, LEED AP BD+C Sustainable Buildings & Operations
> Project Manager *
> *Sustainable Solutions Corporation*
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