eQUEST

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All,

I am trying to model a building with a trapezoidal cross section. I
have figured out how to create a polygon geometry with three vertices in
the Detailed Edit Mode (DE), but am wondering if it is possible to
create a polygon geometry with four (or even five) vertices. Any help
would be very much appreciated.

Thanks,

Jason Hendrixson

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Folks:

Please refresh my memory. DOE-2 (thus eQuest) requires for weather, at a
minimum:

1) Dry Bulb Temp
2) Wet Bulb Temp
3) Wind direction
4) Wind Speed
5) Cloud cover

World geometry develops the sun angle and insolation values (as I
recall).

The modeler takes an existing locale close to where you need the
weather, takes an actual year of as much of the above 5 categories as
one can, and inlays the actual year info over the TMY year (make sure to
call the new file something else !!).

If I leave the Wet Bulb column blank and add Dew Point temperature
instead, is DOE-2 smart enough to generate Wet Bulb from the Dry
Bulb/Dew Point numbers ??

Thanks.

John R. Aulbach, PE, CEM

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John-

I am not certain but I do not think DOE2 can generate the values for
you. Again not certain, but I think the minimum inputs are:

-Dry bulb Temperature (?F)
-Wet bulb Temperature (?F)
-Atmospheric Pressure (inches of Hg times 100)
-Wind Speed (knots)
-Wind Direction (compass points 0-15, with 0 being north, 1 NNE, etc.)
-Cloud Amount (0 - 10, with 0 clear and 10 totally cloudy)
-Cloud Type (0, 1, or 2)
0 is cirrus or cirrostratus, the least opaque;
1 is stratus or stratus fractus, the most opaque; and
2 is all other cloud types, of medium opacity
-Humidity Ratio (pounds of water per pound of dry air)
-Density of Air (lb/ft3)
-Specific Enthalpy (Btu/lb)
-Rain Flag (0 means it is not raining; 1 means it is)
-Snow Flag (0 means it is not snowing; 1 means it is)

DOE2 does not require solar variables but they will provide more
accurate results.

Steve

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Thanks Steve:

The US National Oceanic and Atmospheric Administration (NOAA) can give us years of weather data, but apparently with Dry Bulb and Dew Point. That's why I am trying to use these, without another 8,760 calculations to get Wet Bulb..

John

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Hussein,

I'll admit that I didn't even know what the balance point temperature
was. I did some quick internet research and found this resource:

http://arch.ced.berkeley.edu/vitalsigns/res/downloads/rp/balance_point/b
alance_point_big.pdf

There is a lot of information about building heat gains and losses and
how degree days are calculated. It mentions on p.55 that the 65F number
was determined in the 1940s, and that newer, better insulated homes have
a lower balance point, but it doesn't suggest a number.

William Bishop, EIT, LEED(r) AP

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John-

I am not certain but I do not think DOE2 can generate the values for
you. Again not certain, but I think the minimum inputs are:

-Dry bulb Temperature (?F)
-Wet bulb Temperature (?F)
-Atmospheric Pressure (inches of Hg times 100)
-Wind Speed (knots)
-Wind Direction (compass points 0-15, with 0 being north, 1 NNE, etc.)
-Cloud Amount (0 - 10, with 0 clear and 10 totally cloudy)
-Cloud Type (0, 1, or 2)
0 is cirrus or cirrostratus, the least opaque;
1 is stratus or stratus fractus, the most opaque; and
2 is all other cloud types, of medium opacity
-Humidity Ratio (pounds of water per pound of dry air)
-Density of Air (lb/ft3)
-Specific Enthalpy (Btu/lb)
-Rain Flag (0 means it is not raining; 1 means it is)
-Snow Flag (0 means it is not snowing; 1 means it is)

DOE2 does not require solar variables but they will provide more
accurate results.

Steve

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Thanks Steve:

The US National Oceanic and Atmospheric Administration (NOAA) can give us years of weather data, but apparently with Dry Bulb and Dew Point. That's why I am trying to use these, without another 8,760 calculations to get Wet Bulb..

John

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Could you please help. Is there any recent data or survey about the balance
point temperature of homes in the US. Is the 65F still applicable?
I appreciate any input.
Dr. H. Abaza
ECU

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Hussein,

I'll admit that I didn't even know what the balance point temperature
was. I did some quick internet research and found this resource:

http://arch.ced.berkeley.edu/vitalsigns/res/downloads/rp/balance_point/b
alance_point_big.pdf

There is a lot of information about building heat gains and losses and
how degree days are calculated. It mentions on p.55 that the 65F number
was determined in the 1940s, and that newer, better insulated homes have
a lower balance point, but it doesn't suggest a number.

William Bishop, EIT, LEED(r) AP

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There is degree day data out there for a 55F basis.? But, I haven't used this type of data in a long time though (10 or 15?years?).? At that time at least, 55F?was considered to be a more up to date balance point temperature.

----- Original Message ----

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In my experience from analyzing utility usage data with a floating balance
point, the typical effective heating balance point in US homes will usually be
in the range of 54F - 62F (for true heating climates). Newer homes are usually
closer to the low end of the scale while older homes are on the higher end.
Electrically heated homes tend to be on the lower end but it's not clear how
much of that difference is the effects of vintage/thermal integrity vs. lower
thermostat set points or zoning.

There may be some published results in ACEEE summer study proceedings, but I
can't recall any specific reference.

Michael Blasnik

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Hussein,

If my understanding on this issue is clear, then for heating it is the
statistically-determined ODB temperature at which the heating load on a
building approaches zero. I agree with Mr. Bishop about 65F being
outmoded because I have studied both short and long term end-use metered
data and performed the regressions for single family detached residences
in Florida and New England (USA), both for old and new homes.

This balance point may be somewhat useful on a global basis in analyzing
the heating performance characteristics of typical homes, but for
individual homes the variance can be large, with most homes falling
within the range of about 50 to about 65 degrees F, and a few homes
beyond those limits. The "tighter" the home, the lower the balance
point.

The balance point will also vary with time of day as the internal and
solar heat gains vary (say, from daytime to nighttime).

If you are looking for an overall degree-day (from daily average
temperatures) base, I would recommend something on the order of 55
degrees F for newer homes and 60 for older homes. These will put you
closer to reality for average homes. If you define degree-days from
hourly data as degree-hours per day divided by 24, you will need to use
even lower base temperatures (around 50) for heating and higher (around
70) for cooling.

I wish you good luck with such a "slippery" number, and I hope this
helps. There really are no precise numbers to offer you for specific
applications. And I do not recommend applying these numbers or this
method to large commercial buildings at all.

Glenn Haynes, PE

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Dr. Abaza :

The TREAT (Targeted Residential Energy Analysis Tool) whole building
energy simulation software package can determine a building's balance
point (both heating and cooling) given the building description. One can
construct a 'simple' model of a typical house in about 15 minutes, and
TMY2 weather files for all 50 states are included for driving the
model. It would be pretty simple to make some parametric runs varying
both climate and envelope /infiltration to produce a range of balance
point temps. We have found both insulation levels and air infiltration
(tightness of the envelope) often have the greatest effect on the
balance point of a given structure, along with the temperature setpoints
used for heating and cooling. Significant internal gains, of course, can
also drive the balance points.

A 30 day fully functional version (free download) of the TREAT software
is available from http://www.treatsoftware.com

Best,

Chris Balbach, PE, CEM

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We looked at balance temperature in my Master's Thesis at the UW-Madison
Solar Lab back in 1992. It was sponsored by the Wisconsin Center for Demand
Side Research (now the Energy Center of Wisconsin). Balance temperature was
not the main focus of our research, but we examined interval gas consumption
for a sample of about 100 homes - all from a Midwestern city. The data was
on a 5-minute basis. I can't recall how the sample was determined, so I'm
unsure how representative was the mix of homes. They were from a variety of
sizes, but it looks like most of them were built in the 80s, so they were
newish homes at the time. The average balance temp was about 65F. I'm not
sure the spread around that mean.

Kevin Warren, P.E., CEM, LEED AP

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I have been working on developing an analysis tool that extends the
building passive envelope season based on a dynamic balance point
analysis (see attached)

Vikram Sami, LEED AP

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Vikram -

The balance point tool looks extremely useful during the building design stages when it wpould be much more practical than a detailed energy model.
I look forward to its availability.
Do you intend it to be for commercial as well as residential buildings?
In that case it would need a way to input code-required minimum ventilation rates with some heat exchange options.
The formula Qint = M*Cp UAbld x (Tdes-Tbal) looks odd. Maybe I don't understand the units, but should that be Qint = (M/hr*Cp + UAbld) x (Tdes-Tbal)?

Thanks,

Dave Bryan

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David,
Thanks for pointing that out - there is a typo in the paper. The formula
should read

QSOL + QEQU + QPPL = (M*CP + UABLD) x (TDES - TBAL)

The software uses the correct formula though. At this point we (Lord
Aeck Sargent & The Rocky Mountain Institute) use this as a schematic
design tool on quite a few projects, and find its quite useful. The plan
is to ultimately make this available freely (I would like to make it
work with the new TMY3 files before I start giving it away though).

Once again - thanks for pointing out the typo - sharp eyes (sharper than
mine when I was typing out the paper at 2am).

Vikram Sami, LEED AP

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