06-06
C. SYSTEM CONFIGURATION: As far as possible, provide a common heating
system for all heating terminal units and for the unit mounted
preheat coils for which there is no danger of coil freeze up. With a
common heating system for perimeter heating and interior reheat
applications, care must be taken to ensure that the hot water
temperature, reset schedule, and the flow rates can satisfy perimeter
and interior duties with by selected parameters. Two independent
heating systems, one for interior reheat and another for perimeter
heating, shall be considered only if such an arrangement is proved
cost effective.
D. SYSTEM CONTROLS:
1. Temperatures: The maximum hot water temperature, to meet the peak
heating demand, shall not exceed 80 C (180 F). The hot water
temperature shall be on an inverse reset schedule with the outdoor
temperature and the minimum hot water temperature shall not be
less than 58 C (140 F). The modulating steam valves installed on
the convertors shall operate in response to a change in the
leaving temperature as shown in VA Standard Detail No. 15900-3.
2. Pump Control: The pump(s) shall be allowed to ride on the pump
curve during part load conditions. Care shall be taken to ensure
that at least 15% water flow remains in circulation and water
flows up to the end of each water branch (or a riser). With two
pumps of 50% in operation, staging of the pumps shall be based on
the actual flow and/or outdoor temperature.
4.3 MISCELLANEOUS HEATING APPLICATIONS
Where the outdoor winter design temperature is 4 C. (40 F) and below,
a thermostatically controlled, forced air, heating terminal device(s)
shall be provided for the building entrances, vestibules, attic
spaces, and exterior stairs. In addition, the vestibules shall be
pressurized by supplying conditioned air at the rate of .52 m3/min./m2
(2.0 CFM per square foot) and allowing it to exfiltrate outside by not
providing any ducted exhaust or return air connections.
4.4 PREHEAT COILS (FREEZE PROTECTION)
For situations, where the preheat coils located in the air handling
unit casings could be subjected to below freezing temperature, either
the steam preheat coils with integral face bypass dampers or a
separate heating system with hot glycol water heating coils shall be
used.
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