March 8, 1996

Dehumidification Pays Dividends
Liquid Pressure Amplifiers' Hy-Dry Coil Significantly Reduces Building Humidity Levels
By John Bergfeld

The patented Hy-Dry (TM) System
One function of an Air Conditioning system is to remove moisture from the air. In many areas, it may be the most important function of the system. This moisture removal can consume more power than cooling the air. It is for this reason that Hy-Save Inc. studied different methods of humidity control and developed the Hy-Dry(TM) System. This technology will not only out perform other methods, but will do it in a cost effective manner and generate a very good return on investment.

Theory of the Hy-Dry (TM) System
In an air conditioning system it is the evaporator that removes the moisture. It would therefore seem reasonable that increasing the efficiency of the evaporator would increase the ability to remove moisture. On many systems, a second step in dehumidification is to reheat the air in order to further lower the relative humidity after removing the moisture. If both of these functions can be accomplished at the same time, the desired operation is greatly enhanced.

Hy-Save Inc. addressed these two components of the dehumidification process by utilizing the LPA (Liquid Pressure Amplification) Technology to pump the liquid refrigerant through a subcool/reheat coil placed downstream from the evaporator (Figure 2). In this manner, liquid refrigerant is deeply subcooled on it's way to the expansion valve (TXV), resulting in a dramatic improvement in evaporator performance and moisture removal. At the same time, the heat removed from the liquid refrigerant is used to reheat the supply air stream which reduces the relative humidity of the air delivered. Low dew point subcooling/reheat coils have in fact been used for years, but only through the use of the LPA technology to overcome the pressure losses through the liquid line and subcool/reheat coil can this be accomplished without a significant loss in capacity.

Figure 1

First let us look at a pressure enthalpy chart (Figure 1) to see what is happening. For this analysis, we will use the standard 105 degree condensing temperature with the same liquid temperature. Depending on the size of the Hy- Dry (TM) coil, liquid should be able to be sub cooled to within 5 to 8 degree F of the air temperature leaving the evaporator. As a rule, this will gain 0.5% capacity increase for each degree of subcooling, and that capacity increase is clearly outlined on the pressure enthalpy chart. As an example, with 60 degree F leaving air, we should be able to subcool the liquid to 68 degree F. With 105 degree F normal liquid temperature, this would be 37 degree F of subcooling, or a capacity increase of 18.5% (this capacity increases is a direct result of the cooler refrigerant).

Figure 2

As the liquid exits the TXV, a certain portion will boil off just to cool the refrigerant to the saturation temperature. This flash off of liquid only cools the refrigerant and does not remove heat in the evaporator. However, the compressor sees it as additional work and must still compress this vapor. The colder the entering refrigerant, the less excess vapor there is to be recompressed. In addition, as can be seen on a pressure enthalpy chart, the percent quality of the refrigerant improves from about 72% liquid without subcooling to about 83% liquid with the Hy-Dry (TM) coil in operation. So that is how subcooling helps remove more moisture from the air and the next step is reheat.

Computer rooms and other applications that require strict relative humidity control have long used reheat. Essentially, the air is over cooled to remove moisture and then reheated to raise the temperature back to the set point. This process of reheating also provides a lower relative humidity air. This technique is energy intensive since added cooling is required and energy to reheat the air is required, one might say a lose-lose energy situation. With Hy-Dry (TM) it is a win-win energy situation. The heat is removed from the refrigerant (subcooling = win). and is used for "free" reheating (lower relative humidity = win). No extra or external energy is used. So from all the above it should be clear why Hy-Dry (TM) combines win-win factors to improve overall system efficiency.

Theory and calculations are fine but do they really work? Hy-Save Inc. built a working model to test the Hy-Dry (TM) theory. The unit was monitored every 60 seconds using a data logger. Most of the calculations proved to be quite accurate, however the moisture removal capabilities had been greatly underestimated. The test found that at 65% relative room humidity 50% more water was removed with the Hy-Dry (TM) system than without the Hy-Dry (TM) coil. In order to further check for moisture removal, the condensate water leaving the coil was captured and weighed, verifying the data logger results. At the same time, reductions in head pressure and suction pressure were also observed. The icing on the cake was that this increase in performance was achieved with a reduction in energy consumption of about 12%.

In order to provide certified ratings, a manufacturer must have the performance of the equipment evaluated at a National Testing Laboratory. These test are done under ARI standards of 80 degrees F Dry Bulb and 67 degrees F Wet Bulb temperatures of the entering air. The laboratory results for one manufacturer's equipment showed at 50% relative humidity entering air, 44% more moisture is removed with the Hy-Dry (TM) system.

The manufacturer of this line of AC equipment conducted test of Hy-Dry (TM) at their facilities prior to sending it out for certification. These test were conducted with 35% relative humidity entering the evaporator. Under these conditions over 200% more moisture was removed when compared to the same system without the Hy-Dry (TM) system operating.

The Hy-Dry(TM) system moved from the working model into the field with several applications installed in the State of Florida. The results were again better than predicted with dramatic reductions in relative humidity accompanied by reductions in energy consumption.

At the Florida Department of Health and Rehabilitative Services (HRS) Crystal lake Service Center in Pompano Beach, Florida; six brand new Trane 30 Ton and one 40 Ton split package units were retrofitted with the Hy-Save LPA(TM), Liquid Injection, and Hy-Dry (TM) Technology. During ambient conditions of 89 degrees F dry Bulb and 83% RH, the monitoring showed a 32% reduction in relative humidity inside the building from 66% to 45% relative humidity (RH).

An installation at the North Marion High School in Sparr Florida, showed a 67% increase in total cooling BTU's, a 49.7% decrease in KW per Ton, and a 20% overall reduction in RH, all of which was accomplished under ambient conditions that went from 35% RH during the monitoring before retrofit to 90% RH after installation. Monitoring by the local Utility, Florida Power Corp. showed a decrease in KW demand of 22%.

High relative humidity is a major contributor to what has come to be know as the "sick building syndrome". The Hy-Dry (TM) system will lower relative humidity in the cooling duct delivery system helping to prevent the growth of mold, bacteria and other biological contaminants.

When the relative humidity is lowered with the Hy-Dry (TM) system the thermostat can be raised while maintaining occupant comfort levels. This reduction in load on the compressor can translate into 2.5% savings or more for each degree thermostats are raised. In supermarket applications, reduced humidity levels will reduce the refrigeration loads, reduce the number of defrost cycles necessary, and reduce the need for anti-sweat heaters.

The installation of the Hy-Save LPA (TM) and Hy-Dry (TM) technologies is far less than competing technologies. Heat pipe installation is around twice the cost and a typical Desiccant Wheel system is four times the cost. The Desiccant Wheel also requires higher energy costs after installation to remove the moisture. Installation of the Hy-Dry (TM) system is relatively simple, requiring only one extra coil, an LPA (TM), and some piping. Disruptions to existing operations is minimal.

The Hy-Dry (TM) system increases capacity by as much as 20% and requires no additional fan horsepower. Heat Pipe technology will reduce capacity and may require the use of additional fan HP. Some form of heat is required to dry out the desiccant wheel and this is added energy that is above refrigeration energy use.

Humidity is a major factor in determining the comfort zone for occupants. Reducing the relative humidity through the use of the (TM) system will increase the level of comfort.

The LPA (TM) floating head, Liquid Injection and Hy-Dry (TM) systems will allow cooling equipment to operate at maximum efficiency throughout the year, costing less to do a better job. The Hy-Dry (TM) system does not have the high maintenance and operational cost associated with some competitive technologies and will in fact extend the life of compressors by allowing them to operate at reduced head pressures and temperatures.

By-Line: John Bergfeld is on the Board of Directors of APEC (Association of Professional Energy Consultant) which has a goal of "Bridging the Technology Gap" by providing technology transfers of information.