Surprised?? Read on.


Particularly those used in Chilled Beam & Radiant Panel HVAC systems
Chilled Beam HVAC systems are rapidly gaining acceptance in the North American market because of their exceptional energy efficiency. Critical to this acceptance is the ability to control their tendency to generate unacceptable condensation "rain" from their overhead components.  Condensation sensors are placed on those components to signal the system's control computer to stop or adjust the coolant flow to avoid that "rain".  This has generated an increased interest in condensation and condensation sensors ... and much confusion.

A major contributor to this confusion is the definition of the word “condensation”.   Technically, condensation is the process of changing from a gaseous state to a liquid.  In the chilled beam HVAC world, that will be water vapor in the air condensing on the cooler components as liquid water.   Unfortunately, it has become acceptable to refer to that water as condensation when we all know that technically
– it’s “condensate”.

In chilled beam HVAC systems, we want to control the condensation process so we never see condensate ... the dreaded "rain".  Chilled beam system designs use dew point measurement as the primary condensation control input to the computer control system.  As indicated above,  they will include condensation sensors (sometimes called condensate sensors) as a "safety back-up" input signal to the primary control system.

Back to the "condensation" 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 BASED SENSORS  The most common of "so-called" condensation sensors are actually humidity sensors - or humidistats, that are set to a high RH (Relative Humidity) threshold … typically 90% ...sometimes as low as 80%.  If their specs include "% RH" or "humidity", they are almost certainly this type.  They are mounted on the cold water inlet to the heat exchanger.  When air adjacent to the sensor reaches their pre-set RH threshold, it signals that a condensation condition exists ... it doesn't!  

This signal 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 drops a few more degrees, condensation may occur.
But then again, it may not.  And, it may never have occurred at all.

Regardless, when that pre-set RH threshold is reached, coolant flow is stopped even though condensation is not happening 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. 

Incidentally, there are some manufacturers offering these pipe mounted humidity sensors as "dew point sensors".   These are far short of actual dew point sensors, but that's another subject.  However, it does demonstrate the confusion about condensation in the HVAC industry.

CONDENSATE SENSORS  Another type of so-called “condensation sensor” waits until condensate actually wets the pipe or heat exchanger.  These are really condensate sensors.  Typically, 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.  When condensation is signaled, the pipe and/or heat exchanger is already wet.   We don't want that !! 

While this approach seldom leads to a premature or needless shut down of coolant flow, that pipe or heat exchanger is quite wet and may remain 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 super critical applications.  These include 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 2007, we were approached by a leading architect firm asking if we would develop a configuration of this patented concept specifically for application to chilled beam and radiant panel HVAC systems.  As with any new product development, there were a few mis-steps before we got it just right for this application.  Now, the CONSENSOR is accepted as the industry standard.  The most current version of the resulting product is the Model CG-ICM series found on our web site  here.

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 and heat exchanger are 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.
See the YOUTUBE video at the end of this material.

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 our "ICM", 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.  It is also able to determine if the overall sensor is functioning properly.  If it isn’t, a “SENSOR FAULT” condition will be indicated by the CONSENSOR's on-board LED.  It constantly indicates just what is happening at its location.  It indicates 3 states:


No condensation occurring       Condensation onset is detected          The Sensor is unreliable 
This is a great aid for the installer and for on-site troubleshooting. 

FAIL SAFE TECHNOLOGY   All CONSENSORs incorporate the best "Fail Safe" design techniques.   If an internal failure  (a Sensor Fault) is detected, the output signal goes to a CONDENSATION state.  The CONSENSOR will not allow coolant flow to continue while it is unreliable.  The CONSENSOR's current condition will always be indicated by its on-board LED.

COST  Cost is always a factor.  When all factors are considered ... installation, accessories, etc., THE CONSENSOR MODEL CG -ICM series may cost a bit more than the inexpensive sensors, but in nearly all applications, they are in effect, an insurance policy ... almost always to protect costly equipment, furnishings, etc. from water damage.  In the overall system cost, they are almost a trivial cost factor.

The CONSENSOR has become the industry standard in the HVAC industry.  Our customers include SIEMENS, JOHNSON CONTROLS, TRANE, HONEYWELL,etc., etc.  Many architect firms specify it.   Some chilled beam manufacturers suggest it to customers.

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.
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