[BLDG-SIM] Data source for cold water inlet temperatures

[Joe Huang]

Jason,

I have three thoughts on this :

1) time delay in water temperatures compared to air temperatures. Have you
tried comparing the inlet water temperatures to monthly average temperatures
or degree-days from previous months ?   Assuming that the water pipes are
underground, their temperatures might be closer to soil temperatures 1 meter
or 2 meters down.  For those soil temperatures, the time lag from air
temperatures would be 1 month or 3 months, based on some foundation analysis
work I've done recently.

2) distance from where the water comes from. If the source is far away, the
inlet water temperature will be a composite of the air (or soil)
temperatures at the source and site. For example, water in San Francisco
comes from the Sierras, so I would assume the water temperature would be
significantly colder than San Francisco air or soil temperatures.  In your
regressions, you might take those cities out or add in a second term for the
air or soil temperatures at the water source.

3) there are a few places where the ground temperatures are significantly
higher than air temperature due to geothermal sources. I don't know if any
of the cities in the handbook falls in this category.

I would guess you should be able to get R2 much better than 0.4-0.6, more
like 0.90 or so.  This is just purely a guess on my part.

Joe

----- Original Message -----
From: "Jason Glazer" <jglazer at gard.com>
To: <BLDG-SIM at gard.com>
Sent: Thursday, February 27, 2003 12:15 PM
Subject: [BLDG-SIM] Data source for cold water inlet temperatures


> I received many suggestions for data sources for cold water
> inlet temperatures but the best was:
>
>   EPRI TR-100212, December 1992, "Commercial Water Heating
>   Applications Handbook" by D.W. Abrams & Assoc.
>
> I did some analysis of that data with NCDC degree day and
> average temperature data.  Generally, the conclusion I came
> to is that average monthly and annual temperatures are no
> better at predicting inlet temperature then heating degree
> day data.  That is the not what I expected. The R2
> (goodness of fit) that I was getting are in the 0.4 - 0.6
> range, not very good but expected.  Here are the equations
> I'm planning on using:
>
>   maximum inlet temp = -0.002860 * HDD + 87.8
>
>   average inlet temp = -0.003161 * HDD + 74.3
>
>   minimum inlet temp = -0.003135 * HDD + 59.3
>
> Where HDD is the annual heating degree days base 65.
>
> As you can see the slopes are about the same but the y-
> intercepts are different.  For those who want to explore
> the number some more, my spreadsheet is attached.
>
> Thanks to all who gave me references!
>
> Jason
>
>
> On 23 Dec 2002 at 16:11, I wrote:
>
> > I'm looking for a data source for typical inlet water
> > temperatures (water main temperature) for residential
> > service water heaters for locations in the United States.
> > This is roughly equivalent to the ground temperature at 6 to
> > 8 feet depth. The temperature varies seasonally so knowing
> > the average monthly value would be best.
> >
> > I am already aware of two sources of data that don't really
> > help: Engineering Weather Data from NCDC has the 50 ft
> > temperature and the map in the old ASHRAE Load Calculation
> > Manual is for depths of 4 inches.
> >
> > Any leads would be appreciated.
> >
> > Jason
> >
> > =========================================================
> > Jason Glazer, P.E.  mailto:jglazer at gard.com  847 698 5686
> > GARD Analytics - http://www.gard.com/ 1028 Busse Highway,
> > Park Ridge, IL 60068 Building Energy Simulation and Analysis
> > Admin of BLDG-SIM list for building simulation users
> >
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>
> =========================================================
> Jason Glazer, P.E.  jglazer AT gard DOT com  847 698 5686
> GARD Analytics - http://www.gard.com/
> 1028 Busse Highway, Park Ridge, IL 60068
> Building Energy Simulation and Analysis
> Admin of BLDG-SIM list for building simulation users
>
>
>
>
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