[BLDG-SIM] Data source for cold water inlet temperatures
Jason Glazer
jglazer at gard.com
Thu Feb 27 13:40:09 PST 2003
On 27 Feb 2003 at 13:22, Joe Huang wrote:
> 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.
I don't have any more data then the max, min and annual
average inlet water temperature so I don't know the lag
effects. One to three months seems reasonable and matches
my intuition.
>
> 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.
>
Sounds reasonable but I don't have any knowledge of the
water sources.
> 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 wonder of those places purposely bury their water pipes
as deep as possible to take advantage of the "free water
heater" affect?
> 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.
Given the variation in water supply systems, I think many
details would be needed to reach R2 of 0.90 but it is
certainly possible. Unfortunately, I don't have the
resources to do a survey of water supply systems.
>
> 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. 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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