15 May 2003
UFGS 23 08 00.00 10 requires funding for the designer or a representative of a
designer to participate in the commissioning at the project site.
REFRIGERANTS. Current and anticipated future restrictions limit or prohibit
the use of ozone-depleting substances. ECB 2006-10 and the applicable UFGS have
guidance regarding which refrigerants may be used. Additionally, some Installations
have additional guidance regarding refrigerants. Consult with the applicable
Contracting Officer's Representative to determine applicable guidance prior to the
selecting mechanical refrigeration equipment. Where refurbishment or demolition of
mechanical refrigeration equipment is involved, provide detailed step-by-step guidance
and diagrams that comply with the recommendations of ASHRAE Handbook
Refrigeration in the design.
SPECIAL CRITERIA FOR HUMID AREAS. Use the following criteria in the
design of air-conditioned facilities located in areas where:
the wet bulb temperature is 67 degrees F (19 degrees C) or higher for over 3,000
hours and the outside design relative humidity is 50 percent or higher, or
the wet bulb temperature is 73 degrees F (23 degrees C) or higher for over 1500
hours and the outside design relative humidity is 50 percent or higher, based on 1.0
percent dry bulb and the corresponding mean coincident wet bulb temperature.
System Selection. HVAC systems will typically consist of a central air-
handling unit with chilled water coils or unitary direct expansion-type unit(s) capable of
controlling the dew point of the supply air for all load conditions. In addition to life cycle
cost considerations, the designer must base system selection on the capability of the
air-conditioning system to control the humidity in the conditioned space continuously
under full load and part load conditions. System selection will be supported by a
psychrometric analysis computer program that will consider the latent-heat gain due to
vapor flow through the building structure, to air bypassed through cooling coils, and to
the dehumidification performance of the air-conditioning system under varying external
and internal load conditions. Peak latent load outdoor design conditions (the design wet
bulb temperature and the mean-coincident dry bulb temperature) or low sensible loads
and high latent loads (days with low sensible and high latent external loads) will, in
some cases, cause inside relative humidity to be higher than desired. If analysis
indicates that this condition will occur for an unacceptable period of time, reheat will be
used. Use recovered heat for reheat where possible. Do not use face and bypass
dampers for temperature control.
2-15.2 Air Handling Units. Specify draw-through type air-handling units in order to
use the fan energy for reheat. Design the air distribution system to prevent infiltration at
the highest anticipated sustained prevailing wind.
2-15.3 VAV Units. Use air throttling type VAV terminal units with an integral heating
coil and a pressure independent air valve that modulates in response to space