Condensate pump
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A condensate pump is a specific type of pump used to pump the condensate (water) produced in an HVAC (heating or cooling) or refrigeration system. They may be used to pump the condensate produced from latent water vapor in any of the following gas mixtures:
- conditioned (cooled) building air
- refrigerated air in cooling and freezing systems
- steam in heat exchangers and radiators
- the exhaust stream of very-high-efficiency furnaces
[edit] Construction and operation
Condensate pumps as used in hydronic systems are usually electrically powered centrifugal pumps. As used in homes and individual heat exchangers, they are often small and rated at a fraction of a horsepower, but in commercial applications they range in size up to many horsepower and the electric motor is usually separated from the pump body by some form of mechanical coupling. Large industrial pumps may also serve as the feedwater pump for returning the condensate under pressure to a boiler.
Condensate pumps usually run intermittently and have a tank in which condensate can accumulate. Eventually, the accumulating liquid raises a float switch energizing the pump. The pump then runs until the level of liquid in the tank is substantially lowered. Some pumps contain a two-stage switch. As liquid rises to the trigger point of the first stage, the pump is activated. If the liquid continues to rise (perhaps because the pump has failed or its discharge is blocked), the second stage will be triggered. This stage may switch off the HVAC equipment (preventing the production of further condensate), trigger an alarm, or both.
Small pumps have tanks that range from 2 to 4 litres (0.5 to 1 gallon) and are usually supported using the flanges on their tanks or simply placed upon the floor. A plastic impeller in a molded volute at the bottom of the pump provides the pumping action; this impeller is connected to the motor via a metal shaft that extends downwards from the motor mounted above the tank's top. Large pumps are usually pad-mounted drawing liquid from a tank (sump) below the floor. The smallest pumps may have no tank at all and are simply placed within a container such as the drip pan of a dehumidifier appliance.
In industrial steam systems the condensate pump is used to collect and return condensate from remote areas of the plant. The steam produced in the boiler can heat equipment and processes a considerable distance away. Once steam is used it turns to hot water or condensate. This pump and possibly many more around the plant returns this hot water back to a make-up tank closer to the boiler, where it can be reclaimed, chemically treated, and reused, in the boiler, consequently it can sometimes be referred to as a condensate return pump.
This pump is usually associated with a much larger tank, float switch, and an electric motor than the example above. Some systems are so remote that steam power is used to return the condensate where electricity is impractical to provide.
[edit] The pump output
The output of small condensate pumps is usually routed to a sewer, drain, or the outside world via PVCl plastic tubing. If the outlet of the line is at a higher level than the tank of the pump, a check valve is often fitted at the outlet of the pump so that liquid cannot flow backwards into the pump's tank. If the outlet is below the tank level, siphonage usually naturally clears the output line of all liquid when the pump is deenergized. In cold regions of the world, it is important that condensate lines that are exhausted outside be carefully designed so that no water can remain in the line to freeze up; this would block the line from further operation.
Condensate is not pure water. If it is being condensed from an air stream, it may have dust, microbes, or other contaminants in it. If it is condensed from steam, it may have traces of the various boiler water treatment chemicals. And if it is condensed from furnace exhaust gases, it may be acidic, containing sulfuric acid or nitric acid as a result of sulfur and nitrogen dioxides in the exhaust gas stream. Steam and exhaust condensate is usually hot. These various factors may combine (along with local regulations) to require careful handling or even treatment of the condensate and condensate pumps used for these services must be appropriately designed.
