Dehumidifier with heatexchanger
Comparision in table
Interested in 50 to 78% energysavings ? Read on and check the table.
Dehumidification with only a cooling coil lowered the supply temperature too much.
Than came for the HVAC the cooler with a reheater connected to an external boiler , thus spilling energy for extracting sensible heat and putting it back for about 50%.
Energetically less worse are the systems where the added reheat is coming from the condensor side of the refrigeration machine, which is then partially working as a heatpump: the condensor heat is useful.
In dehumidifiers sold as the plug and play units all the condensor heat is supplied to the cooled airflow, and because the compressor uses 1 kW electric to cool 3 kW it ends with 4 kW in its condensor(+compressor) . Diagram cold cellar
The cooler has to extract heat from the air which is partly sensible and partly latent (water vapour)
When the room temperature is going up the sensible part increases and the dehumidifier will eventually not be able to bring the air to the saturation line. Diagram warmer cellar
With the heatexchanger before the cooler a lot of the sensible heat and even latent heat is taken out of the incoming air and given back to the outgoing airflow thus creating a reheat system where the reheating doesn´t cost fuel and is not effecting the efficiency of the system because there is no compressor needed for moving this amount of energy from incoming to outgoing air.
This system is less sensitive for a rise in room temperature, because the cooler handles mostly latent heat and little sensible heat.
To complete the comparision of the dehumidifier with and without heatexchanger for the above diagrams a table is made and the energy savings are calculated: 50% in case of the cold cellar to 78% in the case of the warmer cellar.
It has to be mentioned that a rise in room temperature also affects negatively the Coefficient of Performance of the refrigerationmachine for both systems.
A firm on the AHR expo in Atlantic City told me that there was a problem in selling an apparatus with in that case a cross flow heat exchanger: the weight of the housing increased and the unit was not easily lifted from a pick-up by one person.
A pity that there was nobody to help him 5 minutes, the spilling apparatus works now for weeks?
And what about car airconditioners?(=cooler + reheater)