TM 5-852-9/AFR 88-19, Vol. IX
glycol systems must utilize mechanical seals to prevent leakage. Glycol in its pure state is a corrosive liquid,
therefore, rust inhibitors must be added to eliminate corrosive effects. Inhibitors break down and deteriorate
at high temperatures, forming a sludge and increasing the solution's corrosiveness. Above 240EF the
breakdown can occur very rapidly. To reduce this breakdown, it is recommended that glycol systems not be
operated above 200EF. Consideration should also be given to substituting other commercially available
antifreeze solutions which are effective and do not deteriorate at higher temperatures, such as heat transfer
oils or antifreeze solutions designed specifically for heating and snow melting systems. These antifreezes,
usually ethylene glycol solutions, contain inhibitors such as mercaptobenzothiazole, disodium, or
dipetassiumphosphates. When using commercial brands of anti-freeze, always be sure to check additive
compatibility. Velocity in heating coils and heating tanks should be kept high enough to prevent extensive
sludge buildup. Small diameter but longer heat exchangers or multipath heat exchangers can be specified for
this purpose. If possible, use straight tube heat exchangers, with removable heads on each end to facilitate
routing sludge from tubes. The straight tube exchanger is recommended, but not mandatory, in lieu of the
more common "U" tube exchanger. If properly sized to provide a 4 to 6-fps fluid velocity in the tubes, "U"
tube heat exchangers are acceptable. Sludge deposits can be particularly bad in heat exchangers or air heating
coils where three-way valves are used to control output because of reduced flow through the tubes under
lighter loads. Gylcol solutions should be checked frequently to maintain a pH of at least 6.4. Due to the
peculiar manner in which water affects glycol ionization, the pH can be varied over a fairly wide range (about
6.7 to 7.7) by adding small amounts of water. It is also good practice to replace glycol yearly. When replacing
the glycol, the system should be completely flushed to remove sludge deposits.
(2) Shop and hangar heating. The frequent opening of large doors and the usual high ceilings in such
buildings can create many heating problems. Some items to be considered are:
(a) Fast heat recovery is necessary in hangars and shops to maintain good working conditions.
The warm building air can be very rapidly displaced when doors are opened, especially when there are strong
winds or cold outside air temperatures. Minimum recovery measured 4 feet above the floor should be from
20EF to 50EF in 120 minutes.
(b) When projection type heaters are used in shops, hangars and other large spaces, units with
sufficient throw and a low discharge air temperature must be selected. Air throw and projection from the unit
should cover the entire floor area. Units selected in this manner will frequently have a larger than required
heating capacity so the quantity of water supplied must be specified and controlled. Installation of overhead
radiant heaters is economical and they should be considered where gas or cheap electric power is available.
(c) Snow melting systems should be installed under hangar doors and ramps to reduce ice and
snow accumulation and keep doors operable. Ramp heating should extend far enough so that vehicle or
aircraft wheels make the transition from ice to bare pavement outside the entrance door.
(d) Radiant heating should be considered for hangar and maintenance shop floors in addition
to the regular heating system. Heat from floor slabs provides greater comfort for workmen.
(e) Infiltration through windows, louvers, and overhead doors is a major cause of building heat
loss in arctic areas. Extreme care in door design and good weather-stripping is required to eliminate excessive
losses. In addition, heat loss calculations must include adequate figures to compensate for infiltration. To
reduce infiltration, operable windows should be kept to a minimum. Window and door construction methods
are covered in chapter 2 in this manual.
(3) Heating control Controls for heating and ventilating systems should generally be automatic.
Manual control systems should also be provided to preclude complete shutdown if automatic controls fail.
Night temperature setback should be considered wherever practical applications exist. Heating coils must
have adequate controls to protect them against freezing. Control systems must be kept simple because expert
maintenance is often not available.
(4) Cooling water and recharge well& Cooling water supply and recharge wells should be
considered where outside temperatures are too high to cool electronic equipment during summer months.
During winter months discharging waste water in recharging wells, rather than on the ground surface, can
effectively reduce ice fog and glaciation. The reduction of ice fog is especially important near airfields. The
temperature of well water in subarctic regions is usually not over 39EF.
(5) Fuel oil design problems.
(a) Fuel oils used in arctic areas should comply with grade DF-A arctic grade as specified under
Federal Specification VV-F-800. Fuel oil meeting this specification has a pour point of -60EF. When used