15 May 2003
round, give further consideration to its use as a supplement to the primary cooling
system when preliminary life cycle calculations show the supplementary system to be
cost effective. For special applications where close temperature or humidity control is
required, consider two-stage evaporative cooling or indirect evaporative cooling in the
life cycle cost analysis as a supplement to, not in lieu of, the primary cooling system.
COMBINATION HEATING-COOLING SYSTEMS. Combine heating-cooling
systems to avoid duplication of system elements and to reduce costs. The limitations of
fan-coil units with regards to latent loads associated with simply providing adequate
ventilation for occupancies such living quarters make them unsuitable as the only
means of cooling and dehumidification in most locations and for most occupancies.
All Air Systems. Where outdoor design temperatures are 20 degrees F (-6
degrees C) or below, consider all air systems only in conjunction with double glazing,
where sedentary activities are a minimum of 3 feet (1 meter) from the glass, and where
proper peripheral air distribution is provided. Use preheat coils whenever the mixture of
return air and ventilation air at outside design temperature is below 35 degrees F (2
All Water Systems. Use two-pipe dual-temperature systems for comfort
applications where feasible. Four-pipe systems may be used where two-pipe systems
are not capable of providing the specified indoor design conditions. Generally, three-
pipe systems cannot be justified for comfort applications and will not be used.
Air-Water Systems. Consider combinations
of air and water systems such
as radiant heating supplemented with single-zone interior air supply for ventilation;
hydronic systems at the periphery of a building to offset skin transmission losses only,
combined with the use of an air system for space cooling and ventilation loads.
Heat Pumps. When considering the use of heat pumps, perform a thorough
engineering analysis. The requirement for possible additional power transmission and
substation capacity, the added impact of demand charge power consumption, and peak
demands must all be evaluated. Select heat pumps on the basis of life cycle cost
effectiveness and include the following types, including combinations, where
ground source heat pumps, using wells or ponds as a heat source or perhaps
imbedding a closed-loop heat rejection circuit in a parking lot as a "heat exchanger."
where the perimeter spaces of a building must be heated and the interior cooled
concurrently, water-to-air heat pumps utilizing a closed-water loop system air
source heat pumps
Radiant Heating and Cooling. Radiant heating and cooling systems are
gaining wider acceptance among HVAC designers. The designer should carefully
review the most current design guidance from both ASHRAE and manufacturers'
literature prior to designing these systems, as they have many unique design