[Equest-users] DHW Savings LEED NC 2.2

[Dahlstrom, Aaron]

Tai:

In general, I tend to follow the procedure laid out in WEc3 for the hot water savings from low-flow fixtures. I've found their calculation procedure for total flow (gallons / year) to be accepted by LEED reviewers.

This does not address water flow from fixtures outside the WEc3 scope, like service sinks, so the ASHRAE handbook or a reasonably documented project-specific assumption sounds like the way to go to get total water use per year for these fixtures.

Like you mentioned, this also does not specify the water temperatures, which are needed for the calc.

Different hot water uses in a building often have different temperature needs (ie handwashing, dishwashing, showers, etc), so even if we know the total water use for each of these fixtures, we'd need to get the expected discharge temperature of each use in order to figure out how much hot water is required.

Most of the time I get the temperatures I need from the project plumbing engineer, who has a better familiarity with these targets than I do.

If you don't have access to a plumbing engineer -

-          For the inlet cold water temp, per the eQUEST dictionary, if you don't specify the temp eQUEST uses the monthly average ground temp. I hope this would be available via an hourly report, although I haven't checked.

-          For the discharge hot water temp, various plumbing codes (IPC, NPC) specify limits on the hot water temp to prevent scalding, and I've seen engineers take a factor off of that to estimate the average hot water use temp. I've heard 110 deg F for showers and 105 deg F for lavs in our office. Service sinks might have something higher (say 120?).

-          For the water storage temp, this is also something that should be obtainable from the plumbing engineer. As a starting point I've heard 120 - 140 deg F in our office as well. I believe the IPC limits the maximum storage water temp to 140.

This should enable you to calculate the quantity (gal / year) of hot water leaving the water heater to serve the annual total flow needed.

Finally, you need to turn the gallons HW / year into a GPM PROCESS-FLOW, if you're inputting into eQUEST. One way to do this is to take whatever use-schedule you had been using (ie eQUEST's default, ASHRAE 90.1-2007 User Manual's, or project-specific) and integrate it, to determine the annual total equivalent full load hours. Dividing total annual gallons by annual full-load hours (and converting units), you should be able to arrive at a GPM to enter as a process flow.

Yours,

Aaron Dahlstrom , PE, LEED(r) AP
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From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Tai Lieu
Sent: Wednesday, June 01, 2011 11:20 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] DHW Savings LEED NC 2.2

Hello  All

We're being audited on the energy model for the dhw saving.  I'm just wondering if this make sense and from your experience if it would be acceptable to the LEED reviewer.

What I've done is taken numbers from ASHRAE Handbook HVAC Applications DHW consumption per fixture for office use.
7.6 L / hr for lavatory fixtures

Showers, kitchen sinks, and Lavatory sinks.
Service sinks I'm not quite sure whether i should include all 5 service sinks (one on each level) or just one sinks since there won't be any mopping done since most of the building Under floor air distribution and i'll do a write up of course to explain my reasoning.

I took the consumptions per fixture numbers multiplied by the amount of fixture then by the demand factor given.

7.6 L/h x 55 # of fixtures x 0.3 demand factor

for each type i took the savings percentage based on each fixture. So baseline is 2.5 and proposed case is .5 for lavatory fixtures

.5 proposed case  / 2.5 base case

So the proposed domestic hot water demand is 25.08 L / hr or 0.11 gpm.

The reviewer had asked for percentage of hot water vs cold water, and temperature at the fixtures, i found that harder to substantiate.  So I thought this process would be a lot better.

Tai Lieu


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