Coil Loop Recovery Systems 2
does not require that the two air streams be adjacent to each
several air streams can be used,
has relatively few moving parts -- a small pump and control valve,
relatively space efficient,
the cooling or heating equipment size can be reduced in some
the moisture removal capacity of existing cooling equipment can
no cross-contamination between air streams.
adds to the first cost, to the fan power to overcome add coil pressure
drop, and for the glycol circulating pump,
requires added glycol pump and piping, expansion tank, and a
three-way freeze protection control valve,
requires that the air streams must be relatively clean and may
Increased ventilation air requirements and rising energy prices
have stimulated interest in heat recovery systems. With heat recovery,
existing system capacity can be increased without adding chiller
or boiler capacity. This system is best applied in buildings where
most of the supply ventilation air and the exhaust air is in one
or two ducts that are not too far apart.
As this system is for sensible heat recovery only, it is best
applied in locations where there is a sizable heating season.
Projects that require a large percentage of outdoor air can increase
system efficiency by transferring heat in the exhaust to either
precool or preheat the incoming air.
Any building where reducing the sensible load on the cooling
equipment is advantageous.
Applications to Avoid
Where there are a number of intake or exhaust air ducts that
must be piped, the benefits are likely not to offset the higher
fan and pump energy and first cost.
Technology Types (Resource)
Coil energy recovery loop systems are highly flexible and well
suited to renovation and industrial applications. The system accommodates
remote supply and exhaust ducts and allows the simultaneous transfer
of energy between multiple sources and uses. An expansion tank
must be included to allow fluid expansion and contraction. A closed
expansion tank minimizes oxidation when ethylene glycol is used.
Standard finned tube water coils may be used; however, these
need to be designed using an accurate simulation model if high
effectiveness values and low costs are to be realized. Integrating
runaround loops in buildings with variable loads to achieve maximum
benefits may require combining the runaround simulation with building
Moisture must not freeze in the exhaust coil air passage. A three-way
temperature control valve should be used that prevents the exhaust
coil from freezing. The valve is controlled to maintain the temperature
of the solution entering the exhaust coil at 30°F or above.
This condition is maintained by bypassing some of the warmer solution
around the supply air coil. If a dual- purpose valve is used,
it can also ensure that a prescribed air temperature from the
supply air coil is not exceeded.
Manufacturer's design curves and performance data should be used
when selecting coils, face velocities, and pressure drops, but
only when the design data are for the same temperature and operating
conditions as in the runaround system.