Building Design and Construction Handbook - Merritt - Ventech!

HEATING, VENTILATION, AND AIR CONDITIONING 13.65
Many liquid solutions are used for heat transmission in solar systems. A typical
solution may be a mixture of water and 10% propylene-glycol antifreeze solution.
It is pumped through the collector tubes in a closed-loop circuit to a heat exchanger,
where the solution transfers its energy to a water-heating circuit (Fig. 13.28a). The
cold glycol solution is then pumped back to the collectors.
The heated water travels in its own closed circuit to a hot-water storage tank
and back to the exchanger. Hot water from the storage tank is withdrawn, as required,
to satisfy building heating requirements.
The hot water may be pumped from the storage tank to another heat exchanger
to produce hot water for domestic use. Hot water from the storage tank may also
be pumped through another closed-loop circuit to a heating coil mounted in a
central heating blower unit for space heating. In both cases, the cooled water is
returned to the storage tank or to the heat exchanger served by the glycol solution.
For use when insufficient solar heat is available, an auxiliary water heater should
be added to the system. Providing hot water for heating and domestic purposes,
the auxiliary heater may be electrically operated or gas, oil, or coal fired.
When solar heat is to be used for cooling, the hot-water loop must be modified.
A three-way valve is placed in the hot-water line to direct the hot water to an
absorption-type water chiller. The chilled water discharge is then pumped to a
cooling coil in the main air-handling unit.
Passive solar systems and attention to solar exposure have had a significant
impact on HVAC design and architecture of buildings. Proper exposures, shading,
and daylighting techniques have gained widespread use.
METHODS OF COOLING AND AIR
CONDITIONING
The methods for establishing accurate heat losses for heating are also applicable
for heat gains and air conditioning. It is mandatory that such procedures be used
in order that the necessary cooling equipment can be sized and selected with the
lowest first cost that will provide reliable and satisfactory service. (See Arts. 13.7
and 13.8.)
13.20 SIZING AN AIR-CONDITIONING PLANT
Consider the building shown in Fig. 13.3 (p. 13.43). Assume only the first and
second floors will be air conditioned. The design outdoor condition is assumed to
be 95�F DB (dry-bulb) and 75�F WB (wet-bulb). The design indoor condition is
80�F DB and 50% relative humidity.
The temperature gradient across an exposed wall will be 15�F (95�F � 80�F).
The temperature gradient between a conditioned and an interior nonconditioned
space, such as the cellar ceiling, is assumed to be 10�F.
Exterior walls are constructed of 4-in brick with 8-in cinder backup; interior
finish is plaster on metal lath. Partitions consist of 2 � 4 studs, wire lath, and
plaster. First floor has double flooring on top of joists; cellar ceiling is plaster on
metal lath.