06-06
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
temperature shall be on an inverse reset schedule with the outdoor
temperature and the minimum hot water temperature shall not be
less than 58 oC (140oF).
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 unless the system capacity
exceeds 7.5 KW (10HP) pump each.
In that case variable speed
drives shall be used.
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 4oC (40oF) 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 36 m3/min. per
sq. meter (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
steam preheat coils with integral face bypass dampers, or a separate
heating system with hot glycol water heating coils, shall be used.
4.5 EMERGENCY ELECTRICAL POWER
The following components of the heating system shall be on emergency
electrical power.
A. All hot water heating pumps.
B. All steam condensate return pumps.
C. All automatic temperature controls, local and central (ECC) control
panels.
D. All hot water boilers if used in place of steam to hot water
convertors.
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