which will be handling 35ºF, or colder, air.
The desired degree of control can be obtained
with a modulating valve on the downstream
coil.
d. Provision should always be made to thor-
oughly mix fresh air and return air before it
enters the coil. In addition, temperature con-
trol elements must be properly located to ob-
tain true air mixture temperatures.
e. As additional protection against freeze-up,
the trap should be installed sufficiently be-
low coil to provide an adequate hydrostatic
head to ensure removal of condensate during
an interruption in the steam pressure. Esti-
mate 3 feet for each 1-psi of trap differential
required.
f. On startup, admit steam to coil ten minutes
before admitting outdoor air.
g. Provision must be made to close fresh air
dampers if steam supply pressure falls below
minimum specified.
Water Heating Coils
1. Water supply and water return connections extend
through the end panel of the coil section. All con-
nections are labeled on the end panel.
2. Water supply and water return connections are
male N.P.T copper pipe.
3. When installing couplings, do not apply undue
stress to the connection extending through unit
panel. Use a backup pipe wrench to avoid break-
ing the weld between coil connection and header.
4. Follow recommendations of the control manu-
facturer regarding types, sizes and installation of
control valves.
5. Hot water coils are not recommended for use with
entering air below 40ºF.
6. If fresh air and return air are to be heated by a hot
water coil, care should be used in the design of
the system to assure thorough mixing before air
enters the coil.
JOHNSON CONTROLS
32
FORM ET102.19-NOM1
ISSUE DATE:08/26/2013
SECTION 4 - PERIODIC MANINTENANCE AND SERVICE