Building Design and Construction Handbook - Merritt - Ventech!

13.60 SECTION THIRTEEN
TABLE 13.13 Water Equivalent of Snowfall
City
In. per hr
per sq ft City
In. per hr
per sq ft
Albany, N.Y. 0.16 Evansville, Ind. 0.08
Asheville, N.C. 0.08 Hartford, Conn. 0.25
Billings, Mont. 0.08 Kansas City, Mo. 0.16
Bismarck, N. Dak. 0.08 Madison, Wis. 0.08
Boise, Idaho 0.08 Minneapolis, Minn. 0.08
Boston, Mass. 0.16 New York, N.Y. 0.16
Buffalo, N.Y. 0.16 Okalhoma City, Okla. 0.16
Burlington, Vt. 0.08 Omaha, Nebr. 0.16
Caribou, Maine 0.16 Philadelphia, Pa. 0.16
Chicago, Ill. 0.06 Pittsburgh, Pa. 0.08
Cincinnati, Ohio 0.08 Portland, Maine 0.16
Cleveland, Ohio 0.08 St. Louis, Mo. 0.08
Columbus, Ohio 0.08 Salt Lake City, Utah 0.08
Denver, Colo. 0.08 Spokane, Wash. 0.16
Detroit, Mich. 0.08 Washington, D.C. 0.16
Table 13.14 gives the required slab output in Btu per hour per square foot at a
given circulating-fluid temperature. This temperature may be obtained once we
determine the rate of snowfall and assume a design outside air temperature and
wind velocity. The table assumes a snow-melting panel as shown in Fig. 13.27.
Once the Btu per hour per square foot required is obtained from Table 13.14
and we know the area over which snow is to be melted, the total Btu per hour
needed for snow melting can be computed as the product of the two. It is usual
practice to add 40% for loss from bottom of slab.
The circulating-fluid temperature given in Table 13.14 is an average. For a 20�F
rise, the fluid temperature entering the panel will be 10�F above that found in the
table, and the leaving fluid temperature will be 10�F below the average. The freezing
point of the fluid should be a few degrees below the minimum temperature ever
obtained in the locality.
Check manufacturer’s ratings for antifreeze solution properties to obtain the gallons
per minute required and the friction loss to find the pumping head.
When ordering a heat exchanger for a given job, specify to the manufacturer
the steam pressure available, fluid temperature to and from the heat exchanger,
gallons per minute circulated, and physical properties of the antifreeze solution.
13.17 RADIATORS AND CONVECTORS
In hot-water and steam-heating systems, heat is released to the spaces to be warmed
by radiation and convection. The percentage transmitted by either method depends
on the type of heat-dispersal unit used.
A common type of unit is the tubular radiator. It is composed of a series of
interconnected sections, each of which consists of vertical tubes looped together.
Steam-radiator sections are attached by nipples only at the base, whereas hot-water
sections are connected at both top and bottom. Steam radiators should not be used
for hot-water heating because of the difficulty of venting.