Accurate Heatloss

Brad White_153

Hi David-

I bought the CD with USAF Engineering Weather Data from a web site affilliated with NOAA. The cost is, when I bought it, $75. It is U.S. Government data hence has no copyright. The data is used by all branches of the military and for public domain use.

Here is a link to the handbook which will explain the terms.
www.ncdc.noaa.gov/oa/documentlibrary/ewdcd/handbook.pdf

It is also attached below.

Use Dry Bulb temperatures for heating design purposes. Those reflect what you feel as a thermometer does (sensible heat). Wet bulb temperatures are what are considered for humidification in winter and dehumidification in summer. Also helpful for determining dewpoints in condensation studies.

Yingomat (System Engineer)

Accurate Heatloss

What temp do you use to get an accurate Heatloss calcualation using Slant/Fin software.
I have done some research on the web and found that the coldest average month in NYC is 24%. The software uses a coldest day. I got following Btu's But I do not which one will be correct.
Indoor temp 72 outdoor 10, water 180. I get 60.819
Indoor temp 72 outdoor 5, water 180. I get 65.732
Indoor temp 72 outdoor 0, water 180. I get 70.645

Cornell Univ. info
New York City, NY 24.7 22.0 in 1977

What temerature do you use for this location?
Thanks in advance.

Brad White_152

Forget

> What temp do you use to get an accurate Heatloss

> calcualation using Slant/Fin software. I have

> done some research on the web and found that the

> coldest average month in NYC is 24%. The software

> uses a coldest day. I got following Btu's But I

> do not which one will be correct. Indoor temp

> 72 outdoor 10, water 180. I get 60.819 Indoor

> temp 72 outdoor 5, water 180. I get

> 65.732 Indoor temp 72 outdoor 0, water 180. I

> get 70.645

>

> Cornell Univ. info New York City,

> NY 24.7 22.0 in 1977 What

> temerature do you use for this location? Thanks

> in advance.

Brad White_152

Forget \"average\" temperature...

Boston's "average" winter temperature is about 40 degrees yet our design temperature is 7 degrees.

Here is some data attached for NY, both LaGuardia and JFK airports. I will post others if I can. These are from USAF weather data which closely follows ASHRAE or the other way around.

The 99.6% column is typically what most engineers use. The "Median of Extreme Lows" is another.

Key is, what is the coldest you would normally expect the temperature to be in any given year? Not the record breakers but rather, the coldest routine temperature that shows up year after year without an OMG!

The typical house can tolerate a cold snap of a few days and if the temperature drops a few degrees inside your house with your boiler cranking at 100%? That means you have a well-sized boiler. Traditionally, most boilers would cycle even then...

Peace Out

Yingomat (System Engineer)

Excellent information.

You are the MAN!!!!

Brad White_152

Glad you like them

Here is Poughkeepsie, Newark NJ and White Plains so you can bracket or average your findings.

Fun stuff!

Brad

D107

great info brad--what's the site url?

Interesting difference depending on the percentage occurrence used. For White Plains, if I'm calculating properly, given 70 inside design and dry bulb 15 outside design (TD 55) at 97.5% occurrence compared with 6 degrees at 99.6% occurrence (TD 64) the variation in heat loss is about 16%.

Should dry or wet bulb temps be used? Seems I've seen wet bulb used more often.

Thanks,

David