Controlling moisture (or humidity) in air conditioned space is an essential function of air conditioning systems. Systems which use mechanical refrigeration remove moisture from the air in the form of condensate, and discharge it during the cooling operation to some remote disposal place such as french drains, storm sewers, and sanitary sewers. Since the sanitary sewer often provides the most convenient place for disposal, it is frequently used for this purpose. Discharging condensate directly into the sanitary sewer, however, introduces a potential health problem; that is, the ingestion of polluted air from the sewer into the air conditioning system.
Air conditioning contractors generally address the problem of air ingestion by installing a trap in the condensate drain line leading to the sewer. This practice, although it satisfies most building and mechanical codes does not resolve the problem satisfactorily. In fact, experience shows that condensate traps create numerous health and operational problems and offer few benefits.
The nature of these problems is determined by the air pressure levels at which the air conditioning systems operate. In this regard, there are two types of systems. In one system, condensate is discharged from a region of negative air pressure. In the other system, condensate is discharged from a region of positive air pressure.
An air conditioning system that discharges condensate from a region of negative air pressure, through a conventional trap, often experiences the following problems:
(a) During the winter months, when the air conditioning system is operating in the heating mode, condensate traps frequently become dry (unless supplied with water from an independent source) and do not provide a seal against the ingestion of polluted air or gases from sewers or other disposal places.
(b) During the first start-up for summer cooling operation (when the trap is dry), condensate cannot flow to the disposal place until the condensate in the collecting tray reaches the level necessary to overcome the negative air pressure in the system. During this initial start-up, and while the condensate tray is being filled, the trap remains dry and there is no seal. In the absence of a seal, polluted air can enter the air conditioning system. At the same time, this air rushes into the condensate tray often entraining condensate, produces condensate blow-over, and sometimes causes the tray to overflow. Since start-up, with an empty trap, usually occurs only once a year, some of these adverse effects may be tolerated but they cannot be prudently ignored.
(c) During the cooling operation, condensate traps frequently become clogged with algae and other foreign materials which originate or collect in the condensate tray. Such clogging and the resulting overflow of the condensate tray is a common cause of water damage in homes and other buildings. To avoid repeated trap clogging, service personnel frequently remove the condensate trap. Such action, when the trap is in a condensate line leading to a sanitary sewer, not only allows the ingestion of polluted air during both the heating and cooling operations, it violates most mechanical codes. Of course, when condensate lines lead to disposal places where the air is not polluted, the absence of a trap creates no pollution problem. However, many such air conditioning systems cannot operate successfully in the cooling mode without a trap, because the high rate of air ingestion often causes condensate blow-over.
Air conditioning systems that discharge condensate through conventional traps, from a region of positive air pressure, are unduly burdened with an operational problem. In this type of system, condensate traps are of little value. Since the air pressure surrounding the condensate collection tray is never negative, it is not possible for the system to ingest polluted air. Hence, if employed in this type of an air conditioning system, as required by most mechanical codes, the trap creates an operational problem of clogging without offering any benefits.
When homes and other buildings are being constructed to conserve energy by reducing air infiltration, air conditioned spaces are becoming more and more susceptible to unhealthy pollution. In this environment, it is at best imprudent to tolerate the installation and operation of air conditioning systems with conventional traps, which offer only a partial seal against the ingestion of polluted air.
Clearly, there is a need for control apparatus that will allow for proper disposal of condensate, and provide protection against pollution, and which, at the same time, is inexpensive and essentially troublefree.