|Abstract or Summary
- The use of a three-pipe distribution system is known to impair
the operating costs of an air conditioning system. Additional costs
are encountered because heating water and cooling water are mixed
in a common return pipe after use by the various air conditioning
units. This investigation covers the design and installation of an
automatic temperature control system to operate a heat pump air
conditioning system utilizing a three-pipe distribution system. The
investigation also was directed toward the study of the economics of
the three-pipe system while in use providing heating and cooling to
an industrial plant.
The experiment was performed with a centrifugal refrigeration
compressor heat pump of 497 tons of refrigeration capacity. Tests
were conducted at outside air temperatures of 42, 51.5, and 53°F.
During each test, heating water flow, cooling water flow, heating supply
water temperature, cooling supply water temperature, common
return water temperature, and cooling return water temperature
were measured. Sufficient data were recorded, during each test, to
determine the heating load, cooling load, and operating penalty due
to the mixed flow condition in the common return. These results
were correlated with outside temperature occurrence data to determine
the additional annual operating cost encountered because of the
use of a three-pipe system.
The additional annual owning cost of a conventional four-pipe
system above that of the three-pipe system was determined. This
cost included items for depreciation, interest, and taxes. A comparison
between the annual owning and operating costs of the three-pipe system and the four-pipe system was made. It was determined
that the three-pipe system installed in the particular industrial plant
investigated exhibits a cost approximately one-third of that of the
conventional system used for comparison.
It was determined that the three-pipe system would become
relatively less costly to own and operate if applied to a system with
similar loads in all areas, if used with a heat pump system, and if
used with a system employing final heat transfer elements selected
for as high a water temperature drop or rise as possible. The
three-pipe system would become relatively more costly to own and
operate if the system piping runs were short, if the individual air
conditioning units were larger, and if a system employing separate
heating and cooling sources was used.