The performance of a wild coil
When no control is exercised over either the temperature or the flow rate of the coolant, a coil is termed ‘wild’. Such an operation may be quite satisfactory, and the method may have economic advantages, since the expense of three-way valves and thermostats is avoided. It is not quite true to assume that no control exists over the temperature of the coolant since, for chilled water coils, the water chiller produces water at a nominally constant temperature. Figure 10.7(a) gives a picture of what happens: as the entering wet — bulb drops, the load on the coil falls, and the mean coil surface temperature reduces, the position of A moving down the saturation curve. However, this will not continue indefinitely. The value of the temperature of the water produced by the chiller is a limiting factor. Under no-load conditions the temperature of A equals this value. So, provided the dew point of the air supplied to the conditioned space may be permitted to drop to such a low value, and that there is no objection to the refrigeration plant which produces the chilled water operating, the wild coil is acceptable. The economic question that must be answered is: will the saving in capital cost, by not using control valves and thermostats, be offset by the extra running cost of the refrigeration plant?
Posted in Engineering Fifth Edition