The increasing acceptance of the highly energy efficient chilled beam and radiant panel HVAC systems in North America has generated considerable interest – and confusion, about condensation sensors used for condensation control.
A major contributor to the confusion is the definition of the word “condensation”. Technically, condensation is the process of changing from a gaseous state to a liquid. In the HVAC world, that will be water. Unfortunately, it has also become acceptable to refer to that water as condensation when we all know that technically
– it’s “condensate”.
To add to the confusion, many reputable manufacturers offer so-called “condensation sensors” that really aren’t condensation sensors at all. It can be hard to identify them. But, the differences can have a significant impact on the HVAC system performance.
Let me address that.
HUMIDITY SENSORS The majority of these so-called condensation sensors are actually humidity sensors set to a high
RH (Relative Humidity) threshold … typically 90% or higher. They are mounted on the cold water inlet to the heat exchanger. When air adjacent to the sensor reaches this pre-set RH threshold, it signals that a condensation condition exists. This is based on the psychrometric chart which indicates that air with this high RH will be very close to saturation. It will be near to the air’s dew point. If the surface temperature of the pipe or heat exchanger in that air drops a few more degrees, condensation may occur.
But then again, it may not.
When that pre-set RH threshold is reached, coolant flow is stopped even though condensation is not happening … and, it won’t happen under these conditions. It’s entirely possible that the dew point would never have been reached. Coolant flow has been stopped on a mere possibility. In areas with typically high summertime humidity, this can be particularly troublesome. It will often mean the needless shut down of cooling capacity when it’s needed most.
CONDENSATE SENSORS Another type of so-called “condensation sensor” waits until condensate actually wets the pipe or heat exchanger. These are really condensate sensors. A copper strip is placed very close – but not in contact with the pipe. These detect the formation of condensate on the pipe by passing a small current from that strip of copper, through the condensate, to the pipe itself. At this time, the pipe and/or heat exchanger is already wet. While this approach seldom leads to a premature or needless shut down of coolant flow, that pipe or heat exchanger may remain a bit wet for very long periods. Unfortunately, air flowing over a wet surface will not exchange its heat to the heat exchanger nearly as well as it will to a bare metal surface. Heat exchange efficiency suffers. Even though this mechanism is different from the humidity based sensors, these also significantly reduce the cooling capacity of the system when efficient heat exchange is needed most. In addition, there is some reason to be concerned about the pipe/heat exchangers being wet or damp for what may be extended periods. That can’t be a good thing !
THE CONSENSOR As you would expect, we have a better way. Before chilled beams and radiant panels came on the North American scene, we had developed a wholly new approach to condensation detection. Our CONSENSOR technology had been used for about 10 years in critical applications including monitoring for condensation in nuclear research facilities, on the MARS ROVER cameras, on water cooled heat exchangers of high power welders, in airborne radar systems, etc. etc. It responds to the onset of the condensation process. In 2004, we were approached by a leading architect firm to see if we would develop a configuration of this patented concept specifically for application to chilled beam and radiant panel HVAC systems. The most current version of that product is the Model CG –ICM series found on our web site at: < http://ChilledBeamCeiling.homestead.com >.
The CONSENSOR is tightly and intimately connected thermally to your cold water inlet pipe near the heat exchanger. It has an internal “Test Surface” that is designed to be very sensitive to the onset of the condensation process. This Test Surface will be thermally the same as your pipe surface. It’s exposed to the same atmosphere. Consequently, the CONSENSOR’s Test Surface will “sweat” at the same instant the pipe begins to “sweat”. In less than a second, coolant flow is stopped … typically before any condensate is visible … but never before the condensation process has actually started.
At most, the pipe will get no more than a light mist of condensate on its surface … usually, not that much. This means that it will quickly dissipate as soon as the conditions allow. Then the CONSENSOR’s indication returns to the normal state – coolant flow resumes. There is no undue delay of the resumption of coolant flow - and the pipe / heat exchanger is dry.
Coolant flow is never interrupted before it’s necessary, and never longer than necessary. Cooling capacity is never needlessly diminished. This is precisely what the customer needs.
COMPANION CIRCUITRY All condensation sensors require a companion electronic circuit to provide a useful signal or output. Most of these circuits are very rudimentary.
In our CG -ICM series, the CONSENSOR is mated with an integrated companion circuit that includes a powerful micro-processor with a sophisticated program. It processes information from its internal Test Surface many times a second and decides if condensation is occurring there. It is also able to determine if the overall sensor is functioning properly. If it isn’t, a “FAULT” condition will be indicated. As an added feature, an on-board LED constantly indicates just what is happening at its location. This is a great aid for the installer and for on-site troubleshooting,
COST Cost is always a factor. When all factors are considered ... installation, accessories, etc. are considered, THE CONSENSOR MODEL CG -ICM series is quite competitive.
THE CUSTOMER The primary advantage of the CONSENSOR approach goes to the customer. The customer always gets full performance from the installed system. There is no fear of condensation "rain". Heat transfer is never diminished because of wet heat exchangers, and cooling capacity is never needlessly cut off when it’s needed most. Use of the CONSENSOR improves system performance under the most critical conditions.
