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The latent heat rate ql is by definition the balance between the total and sensible heat rate above or:
For other condition the ASHRAE Handbook, Fundamentals, must be consulted.
d. Kitchen. Cooking is responsible for both sensible and latent loads. Appliance surfaces contribute
most of the heat in kitchens in the form of radiant energy. Appliance heat loads are detailed in ASHRAE,
Fundamentals.
(1) If the appliance is under an exhaust hood, the maximum heat released to the kitchen due to
radiation is estimated at 32 percent of the rated heat input. With a 50 percent factor for diversity and the
effect of thermostatic controls, the average heat emission in the room is then 16 percent of nameplate
rating in Btuh, and the balance or 34 percent goes to the hood exhaust stream.
(2) For direct fuel fired appliances, a correction factor must be applied because they require 60
percent more heat input than electric or stream equipment of the same type and size, and the heat radiated
in the kitchen is only 10 percent of the rated Btuh input.
(3) For all cooking appliances not installed under an exhaust hood, the heat gain maybe estimated
at 50 percent of the rated input regardless of the type of energy or fuel used. It may be assumed that 34
percent of the heat is latent and 66 percent is sensible.
e. Engines. For diesel and gasoline engines, the only heat gain to be considered as internal load is
the radiated load, estimated at 370 to 400 Btuh per bhp. The heat transferred to the cooling water is covered
in chapter 5. For boilers, the heat radiated intro the conditioned space will be dependent on the temperature
difference between the interior of the boiler and the conditioned space, the overall coefficient of heat
transfer of the boiler plate and insulation, and the surface area of the boiler. This heat gain will have to be
calculated for the specific boiler selected. Proper selection of insulation can reduce this load to a minimal
amount.
f. Miscellaneous equipment. Other equipment using power such as computers, radar, and
communication equipment will also produce a heat gain based on its specific characteristics as indicated
by the manufacturer.
2-7. External load.
a. The sensible and latent heat transfer between the space and its surroundings constitute the
external load. Aboveground, the ambient air is the dominant factor. Solar radiation's influence is
always indirect because of the absence of fenestration in hardened structure. In addition, the thickness of
the walls will reduce considerably the propagation of the external daily temperature variations to the
inside spaces.
b. Moisture seepage through boundaries aboveground will be
eliminated just as it is
for conventional
structures; however, the designer should be aware that the thermal parameters of the overburden used in
mounded-over structures, for instance, are sensitive to moisture content and therefore dependent on local
c. Underground, the structure's environment will, by contrast, vary in texture, contain fissures or
faults, and be subject to hidden hydrostatic and thermal influences. Heat transfer from this environment
is covered in chapter 3. Temperature variations in the underground environment are relatively small
over a period of time compared to the wide ranges of seasonal variations which affect an aboveground
structure.
d. The intrusion of moisture into the underground structure is much more unpredictable and
difficult either to measure or control than in the aboveground structure. Therefore, the design of the AC
system for the underground structure will anticipate relatively constant temperature levels but varying
moisture conditions. Each site will present a unique series of geologic and geographic conditions. No
uniform design procedure can be applied universally to all sites.
e. The underground environment is
exceptionally dominated by
the movement of
groundwater
around the space; but the usual assumption is that this percolation will not eliminate conduction from
consideration and that both transfer mechanisms can be evaluated separately.
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