TM 5-852-9/AFR 88-19, Vol. IX
a. Economical insulation thickness. The cost of supplying fuel to arctic sites is extremely high when it
has to be airlifted. For this reason, a special economic analysis needs to be made to determine the proper
insulation thickness based on a balance between reduced fuel costs and increased construction costs. The
optimum U-value should be determined from a life cycle cost analysis that includes a consideration of all
initial, operational, and energy costs. For buildings where heating loads will be met predominantly by space
heating rather than internal gains, the following procedure is recommended to determine the most economical
insulation thickness. This procedure is based on CRREL Report 82-27. Buildings with significant internal
gains, the potential for using heat exchangers, or complex heating and ventilation requirements should be
subject to a more sophisticated analysis than that outlined below.
(1) Calculate a climate-heating cost parameter (CHC) which will pertain to any building sharing the
same site and heating costs by using the equation 4-1:
CHC = (24) (5/6) (HDD) ((P/B) FC + (P/A) OMC))/FE
(eq 4-1)
where: 24
=
factor converting days to hours
5/6
=
factor accounting for internal heat gain (alter appropriately)
heating degree-days (65EF base)
HDD
=
P/B
=
present worth factor* for escalating fuel costs
FC
=
fuel cost ($/Btu)
P/A
=
present worth factor for uniform series (O&M costs)
OMC
=
plant operation and maintenance costs
FE
=
combined efficiency of plant and distribution system.
*Note: The use of present worth factors is found in National Bureau of Standards (NBS) Handbook 135 and cited in Defense
Energy Program Policy Memorandum 85-2.
(2) Choose a minimum acceptable R-value (Ri) and per square foot construction cost (CCi) for each
construction component (e.g., walls, roofs, exposed floors).
(3) Establish the higher R-values (Rf) and per square foot construction cost (CCf) for each
alternative improvement to the minimum identified in paragraph (2).
(4) Calculate the savings-to-investment ratio (SIR) for each alternative improvement using the
equation 4-2:
(1/Ri & 1/Rf)
SIR ' (CHC)
(eq 4-2)
(CCi&CCf)
(5) Choose the option with the highest SIR.
located within unheated portions of the building should be capable of operating at the lowest ambient
temperature. The lowest operating temperatures for the piece of equipment should be stated in the
specifications. Special low temperature lubricants must be used. Manufacturers should be required to
guarantee their equipment under the extreme weather conditions expected at the site.
c. Air compressors and their operation. The following suggestions for air compressor system operation
and design apply to both instrument air and compressed air in shops and hangars. Water vapor, if not
removed, can freeze and cause the system to quit functioning. Pneumatic control systems require dry air to
function properly. Exterior air should be the air source for large compressors. The cold outdoor air contains
less moisture, and therefore less water must be removed from the system. For example, heated room air at
70EF and 10 percent relative humidity has .0015 pounds of moisture per pound of dry air, while outside air
at -20EF and 100 percent relative humidity has .00025 pounds of moisture per pound of dry air. At these
conditions, the room air has six times as much moisture as the outside air.
4-18
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