Comfort At Work: Case Study

The Use of MoistureMiser Equipped 50HJ's in Fast Food Restaurants

Final Report

MoistureMiser De-humidification Package

September-November 1995

Daniel J. Banks, Commercial Unitary Systems, Tyler, TX

Executive Summary

Carrier's Commercial Unitary Systems group, in conjunction with Carrier of Florida West Coast and BSS, has completed a case study in the Clearwater, Florida area. The focus of the study was to assess the performance of Carrier's new MoistureMiser de-humidification package on decreasing the humidity level in "fast food" restaurants. Three Burger King® restaurants, with comparable architectural designs, were chosen. Each restaurant was equipped with two Carrier 50HJ006 five ton rooftop units in the kitchen areas. One restaurant was equipped with 50HJ's with MoistureMiser options, the second restaurant with Heat Pipes, and the third was installed without any additional dehumidification devices. It was theorized that the MoistureMiser would maintain moisture levels of the air 15-20% lower than that of the standard rooftop equipment and perform equally to the Heat Pipes.

Controlling humidity is an increasingly desirable function of air conditioning equipment. The MoistureMiser increases the latent capacity of the unit, thus increasing the "paid for" cooling effect. This feature is especially desirable in "fast food" restaurants where cooking devices and other kitchen activities create large amounts of moisture in the air that ultimately must be removed. A common method used today to remove humidity from the space is to install Heat Pipes in the roof curb below the unit.

The MoistureMiser is a factory installed de-humidification package on Carrier 48/50HJ 3-12.5 ton rooftops that is designed to increase the latent capacity of the rooftop. This device is activated by a humidistat / solenoid valve control system that controls the MoistureMiser to operate only when needed. This control capability allows the HJ rooftop to maximize either its sensible or latent capacity based upon the load in the space.

The results from the case study demonstrate that the MoistureMiser is a powerful tool for removing humidity in the space. When compared to a standard 50HJ rooftop, the rooftops equipped with the MoistureMiser maintained moisture levels 15.6% lower, while at the same time reduced utility bills by 7%. The MoistureMiser also performs at virtually equivalent levels to the Heat Pipe which is an already proven device in the marketplace. When compared to the Heat Pipe, the MoistureMiser maintained relative humidity levels just 3.9% higher than the Heat Pipe. In addition, the lower initial cost (25-40% that of a four row Heat Pipe) makes the MoistureMiser a cost effective alternative to the Heat Pipe and the preferred choice for dehumidification. This case study has verified the strong latent capacity enhancements that the MoistureMiser brings to Carrier rooftops.

Introduction

Carrier's Commercial Unitary Systems group, in conjunction with Carrier of Florida West Coast and BSS, has recently completed a case study in the Clearwater, Florida area. This report contains the conclusion and recommendations obtained from the study.


50HJ with MoistureMiser



Port Richey Burger King®

The focus of the study was to assess the performance of Carrier's new MoistureMiser De-humidification Package on decreasing the humidity level in "fast food" restaurants. As stated in the executive summary, three Burger King® restaurants, with comparable architectural designs, were chosen. The restaurants were equipped with the new test rooftop units in late July of 1995 and testing began the later half of September. The test was undertaken to prove the extensive latent capacity improvements created by the MoistureMiser and to demonstrate its similar capabilities with the Heat Pipe.

Is Humidity A Concern?

Yes, there are six major reasons why humidity should be a concern. And they are as follows:

  1. Indoor Air Quality - Humidity is a major factor in the growth and promulgation of mold, mildew, and bacteria in a building. Biological growth can spread quickly and grow in carpet, ductwork, and on walls. This problem often supports cases of Sick Building Syndrome. Sick Building Syndrome can lead to increased health care cost and employee sick time. ASHRAE recommends that relative humidity levels be maintained below 70%.

  1. Comfort levels - High humidity interferes with the body's natural cooling process of evaporation at the skin's surface. This can cause occupants to become uncomfortable forcing them to lower the thermostat's cooling set point.

  1. Humidity Damage - Humidity can cause expensive damage to property such as staining wall paper, wood work, and ceiling tiles. It can damage books, artwork, and create strong odors in carpets. Humidity also makes process control difficult in certain industrial/manufacturing environments.

  1. Improper Ventilation - Hot and humid areas present a unique challenge in providing adequate ventilation for buildings due to high humidity levels outdoors. ASHRAE Standard 62-89 states that 20 CFM of outdoor air is required per person. This extended requirement brings additional humid outdoor air into the building making humidity control extremely important.

  1. Equipment Inefficiency - Humidity can cause inefficient operation of refrigerators and freezers.
  2. Increased energy cost - Because of high humidity levels and less comfortable conditions, thermostat set points are lowered to force the HVAC equipment to run longer and work harder to lower the humidity levels.

MoistureMiser Theory of Operation

This Carrier rooftop option provides greater dehumidification by further subcooling the hot liquid refrigerant leaving the condenser coil. The MoistureMiser package consists of a subcooling coil located on the leaving air side of the evaporator coil. The location of this coil in the indoor air stream enhances the latent capacity of the HJ rooftop by up to 40% in certain instances.

This device is activated by a humidistat/solenoid valve control system that controls the MoistureMiser to operate only when needed. This control capability allows the HJ rooftop to maximize either its sensible or latent capacity based upon the load in the space. During operation, the rooftop will attempt to maintain the humidistat set point, but will also respond to the thermostat in the occupied space. When the thermostat is satisfied, the unit will shut down until the next call for cooling.

If the unit is in the cooling mode and the humidistat senses an unacceptable humidity level, the humidistat switch will close. This will energize the liquid line solenoid valve (LLSV), forcing the hot liquid refrigerant to enter into the subcooler coil (See Figure 1). Note: During standard unit operation with the LLSV open, the refrigerant will not enter the subcooler coil due to both the large pressure drop across the subcooler coil and the thermostatic expansion valve (TXV).

As the hot liquid refrigerant passes through the subcooler coil, it is exposed to the cold supply airflow coming from the evaporator coil. The liquid is further subcooled to a temperature approaching the evaporator leaving-air temperature. The liquid then enters a TXV, where the liquid drops to a lower pressure. The TXV does not have a pressure drop great enough to change the liquid to a two phase fluid, so the subcooled liquid enters the Acutrol device at the evaporator coil.

The liquid enters the evaporator coil at a temperature lower than in standard cooling operation. This lower temperature is what increases the latent capacity of the rooftop unit. The refrigerant passes through the evaporator and is turned into a vapor. The air passing over the evaporator coil will become colder than during normal operation. However, as this same air passes over the subcooler coil, it will be slightly warmed.

Included with the MoistureMiser De-humidification Package is a low pressure switch on the suction line. This switch keeps the evaporator coil from freezing during MoistureMiser operation. The low pressure switch will only deactivate and open the LLSV. This in turn only de-activates the operation of the subcooler coil. It will not de-activate the compressors.

With the MoistureMiser circuit de-activated, the operating pressures/temperatures will return (increase) to acceptable levels, and the compressor(s) will continue to operate normally. Once the space thermostat is satisfied and the compressor(s) is deactivated, the low pressure switch will close. This allows the MoistureMiser circuit to operate as necessary on the next call for cooling.
































Figure 1 - MoistureMiser Dehumidification Package
































Figure 2 - Psychrometic chart (48HJ006 Shown)

Referring to the psychrometric chart in Figure 2, it can be seen how the moisture content of the supply air is further reduced by using the MoistureMiser package. Figure 2 shows the entering and leaving air conditions for a laboratory 48HJ006 rooftop with the MoistureMiser both activated and de-activated. Point one represents the rooftop entering air conditions. At point two, the leaving air conditions with the MoistureMiser de-activated, the moisture content is 0.0095 lb. of water per lb. of dry air. At point three, the leaving air conditions with the MoistureMiser activated, the moisture content of the air is .00825. This represents a drop in the moisture content of the leaving air by 13.2%.





















Figure 3 - Pressure-Enthalpy Curve

Without Subcooler coil

The refrigerant cycle for R-22, is shown in Figure 3. Without the subcooler coil activated, the refrigerant follows the typical cycle of a standard rooftop. At Point 1, vapor leaving the compressor at a high pressure and high temperature, enters the condenser. The condenser removes heat, thus lowering the enthalpy/temperature. At Point 2, liquid leaves the condenser and enters the Fixed Expansion Valves (Reamers). This phase lowers the pressure. At Point 3, the liquid enters the evaporator coil, where it absorbs heat from the supply air. At Point 4, the vapor leaves the evaporator and enters the compressor, which increases the pressure and temperature.

With Subcooler coil

The subcooler refrigerant cycle for R-22, is also shown in Figure 3. With the subcooler activated, the refrigerant follows a revised cycle. At Point 1, vapor leaving the compressor at a high pressure and high temperature, enters the condenser. The condenser decreases the enthalpy. At Point 2, liquid leaves the condenser, enters the subcooler coil, and lowers the temperature, thus the name subcooler. At Point 2A, the subcooled liquid enters the Thermal Expansion Valve (TXV), which lowers the pressure to help control the level of superheat. At Point 2B, the liquid enters the Fixed Expansion Valves (Reamers) and leaves as a saturated vapor before entering the evaporator at Point 2C. The enhanced refrigeration effect induced by the subcooler coil is seen to the left of points 2 and 3.

Heat Pipe Theory of Operation

The Heat Pipe is a heat transfer device that uses evaporation and condensation of a working fluid to transfer heat. It relies on the same basic refrigeration principles used by air conditioners. Heat Pipes are completely passive with no energy input required.

A Heat Pipe consists of a sealed tube containing a working fluid, typically R-22. The tube is inclined, so that the liquid refrigerant flows by gravity to one end. Heat is transferred through the movement and alternate evaporation and condensation of the refrigerant. The low end (return air) of the Heat Pipe functions as an evaporator where the liquid refrigerant absorbs heat as it evaporates. The low density refrigerant vapor then rises to the upper end of the tube (supply air). This functions as the condenser and releases heat to condense the fluid into a liquid. Gravity causes the liquid to flow downward to the evaporator and the cycle is repeated.

Figure 4: Heatpipe Schematic of Operation


Field Trial Background

The restaurants chosen for the test are all owned and operated by Mr. Sam Risola of Samar Management in Port Richey, Florida. Topic-Kool Engineering, of Largo, FL, served as the mechanical contractor, while Carrier's Building Systems & Services (BSS) installed and serviced the Carrier Comfort Network Controls. Distribution of the units was through Carrier of Florida West Coast under the direction of Pat McCarthy. The case study monitoring and evaluation was under the direction of Daniel Banks with Carrier Corporation in Tyler, TX.


Burger King® Port Richey

Three Burger King® restaurants which had previously been equipped with Carrier 50HJ006 units and Heat Pipes were chosen for the field trial. The restaurants were chosen because they are in close proximity of each other and therefore experience the same climatic conditions. In addition, the restaurants have similar architectural design and customer traffic patterns. Although not exact, the load levels obtained in each restaurant are comparable.

Each restaurant had two 50HJ006 high efficiency units installed with vertical ductwork connections in the kitchen area. The MoistureMiser units were installed in the Port Richey restaurant. The Clearwater restaurant has standard 50HJ006's with no dehumidification devices installed. The Holiday restaurant has two 50HJ006's with Heat Pipes installed. The Heat Pipes were four row devices that were mounted in the roof curb. All units on the three restaurants were equipped with manual outdoor air dampers that were opened to bring in 20% outdoor air. Finally, all three restaurants have an additional three units without dehumidification devices installed. These units are used to cool the dining areas.

Remote Monitoring Equipment

The equipment used to monitor the air conditioning units is broken down into three groups by location.

50HJ006

An Apollo control module is located in each unit. These communicating control modules and their Carrier programmable thermostats allow input from sensors measuring the Outside Air Temperature (OAT), Return Air Temperature (RAT), and Supply Air Temperature (SAT). In addition, the subcooler control on the Port Richey restaurant is controlled by a relay via the humidistat.

Control Panel

The control panel contains the bulk of the monitoring equipment. A single comfort controller and a data collection module are wired to a common bus per building. These controls feed into an AutoDial Gateway and a Hayes 14,400 BPS modem. The Comfort Controller receives the following inputs: Indoor Humidity, Outdoor Humidity, and Pulsemeter. The Pulsemeter is a power sensing device that converts the analog signal of the rooftop units power supply into a digital signal that the comfort controller can interpret. The data collection module stores the data until the modem can transmit it to the host computer.

Tyler Plant

The Tyler plant is equipped with a Pentium processor based computer, AutoDial Gateway, and a Hayes 14,440 BPS modem. In addition, the Windows NT operating system is used in conjunction with a SQL client server relational database. This combination of operating systems and server provides the platform on which Carrier ComfortWORKS resides and operates. ComfortWORKS was programmed to sequentially poll all three test sites each day at 15 minute intervals. The data collection module stores the data until polled. Afterwards, the data collection modules renew the data collection role. In addition, real time data can be retrieved from the system elements. A schematic is shown in Figure 5.

Architectural Design




Holiday Restaurant Interior

While the size of the Burger King® restaurants tested are equal, the actual layouts are slightly different. The Holiday and Clearwater restaurants have side kitchen layouts, while the Port Richey restaurant has a rear kitchen layout. For this reason, direct comparison between Zone 2 units cannot be made. The loading between Zone 1 units is equivalent. The black squares represent the 50HJ006 rooftop units and the boxes with an "X" identify the units that were outfitted for controls.

















Holiday and Clearwater Restaurants Port Richey Layout

MoistureMiser Equipped




Figure 6: Burger King® Restaurant layouts

Results

The climate data for a typical day in the greater Clearwater area is shown below. One trend of note is the fact that as the temperature increases throughout the day, the relative humidity decreases. The temperature will reach a peak level during the 15:00 to 17:00 time period, just as the relative humidity is at its lowest point.

Condensate Measurements

Measurements of condensate draining from the units were made at both the Port Richey and the Clearwater restaurants. These measurements were made during the same time period commencing at 12:00 noon and continuing for one hour on August 4, 1995. The outdoor temperature during the measurements was 92 degrees F. Both units ran continuously during the one hour period. A similar comparison between the Heat Pipe and both the MoistureMiser and standard units was not made.


Port Richey Clearwater Location



w/ MoistureMiser w/ No De-humidification


Condensate Volume 478.5 oz. 428.0 oz.


% Difference 11.6%


The data illustrates that the rooftops with the MoistureMiser removed 11.6% more water vapor from the air in comparison to the standard 50HJ rooftops. This indicates a remarkable increase in condensate volume. Based on these measurements, we can already conclude that the MoistureMiser provides an effective means of reducing latent air conditioning load.

Relative Humidity

The humidity control capability of the Moisture Miser is illustrated below. The MoistureMiser significantly outperformed the units on the Clearwater restaurant without any dehumidification devices and performed almost equally with the Heat Pipe device.

On average, the MoistureMiser kept the space relative humidity 14 percentage points lower than the restaurant equipped with the standard rooftops and was only 3 percentage points higher than the restaurant equipped with the Heat Pipes.

To fully understand the importance in the relative humidity measurements, we must also look at the amount of water contained in the air. The following chart shows the dry bulb, wet bulb, relative humidity levels, and the pounds of water per pound of dry air in zone one of each restaurant on November 8th at 1:00 p.m.. The outdoor temperature in Clearwater at this time was 87 degrees.
Restaurant Location
Indoor Dry Bulb (F)
Indoor Wet Bulb (F)
Indoor Relative Humidity
Indoor Moisture Content - lb. of water/lb. dry air
Clearwater - standard units
72.0
65.7
72.0
0.01213
Port Richey - MoistureMiser
74.0
63.6
57.0
0.01024
Holiday - Heat Pipe
75.0
63.4
53.0
0.00984

These results confirm the MoistureMiser demonstrates superior humidity control over a standard rooftop unit and virtually matches the performance of the Heat Pipe. The Port Richey MoistureMiser equipped unit controlled its space moisture content at a level 15.6% below that of the Clearwater restaurant with the standard unit. In addition, the MoistureMiser restaurant moisture content was only 3.9% higher than the Heat Pipe. These results verify the ability of the MoistureMiser to improve humidity control and better prevent bacterial growth and property damage.

Power Consumption

As described before, an important aspect of humidity control is monitoring comfort levels. This in turn, allows thermostat cooling set points to be raised which reduces energy consumption. Humidity control and reduced power consumption are both strengths of the MoistureMiser. An important fact that should not be overlooked is that these advantages are not at the expense of uncontrollable temperature in the space. The chart below illustrates this point. The temperatures in the kitchen area are not significantly different than the Heat Pipe or the Clearwater restaurant.

All three buildings had 73 degree F set points and the temperatures were maintained within a 2 degree spread. However, on November 2nd, the Port Ritchey restaurant (MoistureMiser) raised their cooling set points to 76 degrees. After this occurred, a call was made to the Port Richey Burger King® restaurant manager Ms. Judy Mermer to arrange to change the set points back to 73 degrees. Ms. Mermer stated that because of the improved humidity control, the thermostat levels needed to be raised several degrees to maintain a satisfactory comfort level. Phil Ardis of Tropic-Kool engineering, Samar Management's HVAC contractor, whom installs hundreds of Heat Pipes each year, explained that this is a common occurrence after adding de-humidification devices. Mr. Ardis also elaborated that improved comfort levels almost always allow set points to be raised resulting in improved energy savings. The thermostat set point then remained at 76 degrees and the corresponding decrease in power consumption was monitored.

The power consumption of the units tested was affected by the raised set points. The MoistureMiser used less energy than the other two stores. The below chart shows the average power level trends over a 25 day period.

As evidenced in the above chart, the power levels are lower for the MoistureMiser units. Carrier also asked the Port Richey franchise owner Sam Risola of Samar Management on 11/29/95 about his utility bills. Mr. Risola happily stated, "We have noticed, since removing the other rooftop units, a 7% to 8% reduction in our utility bills. This is a nice change."

In addition, compressor run time for the three units was also evaluated. The compressor run time for the MoistureMiser restaurant is seen below. The data shows how compressor run time for the periods eight days before and eight days after November 2nd were altered when the cooling set points on the Port Richey restaurant were increased. This data represents almost a 20% decrease in compressor operation.

Conclusions

In conclusion, the results from the case study confirm the substantial benefits of the MoistureMiser in buildings that require humidity control. The MoistureMiser has proven itself to be an outstanding control when applied in an application with both a humid indoor and outdoor environment. As seen in this case study, the MoistureMiser's advantages provide great benefits for building owners, contractors, and engineers.

Building Owners

When building owners evaluate HVAC equipment, they look at initial purchasing costs, operating expenses, service costs, unit performance, and comfort levels. When choosing a de-humidification system, comfort is by far the most important factor evaluated by a building owner.

In the case study, the MoistureMiser outperformed the Clearwater location with standard units. When comparing the condensate leaving the drain pan of the rooftops over a one hour period, the rooftops with the MoistureMisers removed 50 more ounces of water than did the standard units. This was an 11.6% advantage. The MoistureMiser units maintained the moisture content of the air 15.6% lower than the standard units as well. This reduction results in significant comfort improvements and drastically reduces the risk of property damage and biological growth. Perhaps the overall comfort improvements are best reflected by Mr. Risola in his statement during an interview with Carrier's BEAM Television, "Since we have got those units installed, we have felt quite a difference. The comfort level is much better than what it has been."

As was seen during the testing, the improved comfort levels induced by the MoistureMiser allowed thermostat cooling set points to be raised. This brought about reduced compressor run time and energy savings. As was seen by the Burger King® restaurant, the MoistureMiser decreased the utility bills by 7%-8%. In addition, since the employees raised the cooling set points, compressor run time also decreased by 20%. These operating savings in addition to greatly improved comfort levels can easily justify the purchase of the MoistureMiser De-humidification Package.

When building owners look at purchasing costs, the four row Heat Pipe initial cost is between $250-300/ton. The cost of the MoistureMiser is between $150-200/ton. In accordance with the data from the case study, the extra $50-100/ton for a four row Heat Pipe over the MoistureMiser will only give the building owner an additional 3.9% reduction in water vapor levels. This makes the MoistureMiser a very cost effective competitor. In conclusion, operating savings, cost effective initial costs, and improved comfort levels all lead to a satisfied building owner.

Contractors

Contractors are primarily concerned with ease of installation, start-up, and servicing of rooftop equipment. They prefer simple installation procedures and require components to be easily accessed for service and replacement. In these areas, the MoistureMiser offers some definite advantages to the contractor. As compared to the MoistureMiser, the Heat Pipe has one to three more rows of additional coil which subjects the air to a two to three times larger pressure drop as it passes through the rooftop unit. This can cause some problem with the indoor fan performance of the unit if the system is not designed properly. This makes the MoistureMiser system's air flow easier to balance and therefore, makes the unit easier to install and start.

In this case study, the Heat Pipes were mounted in a roof curb. This required the Heat Pipe to use a secondary filter upstream of the Heat Pipe's return air coil. This was a second filter to maintain and subjected the air flow to yet another pressure drop. Mr. Risola pointed out that since this second filter is usually located in an awkward position in the ductwork, it is difficult for the service contractor to access and maintain. In addition to a second filter, the roof curb mounted Heat Pipe's return air coil is not exposed to the outdoor air that enters the rooftop. This coil is located upstream and cannot pre-condition this hot and humid air. The MoistureMiser subcooler coil is located downstream of the rooftops filter and is exposed to the outdoor air flow so it can be conditioned properly.

Another advantage the MoistureMiser provided for the contractor is that it was delivered direct from Carrier, factory installed and pre-tested. This reduced the complexity of the distribution channel as well as eliminated any additional field labor to install and start this device. The MoistureMiser is designed, tested, and manufactured specifically for Carrier rooftops. One company handles all application support, service, and warranty issues. The contractor only had to deal with one point of contact, Carrier Corporation, when any issues arose.

Consulting Engineers

The MoistureMiser design, as earlier stated, is pre-engineered, pre-tested, and factory installed. All information needed to integrate this equipment into a buildings design is provided by Carrier. Cooling capacity tables that show the rooftops performance with the MoistureMiser both active and inactive are provided. In addition, air side pressure drops, charging charts, trouble-shooting guides, and operating sequences are provided in a MoistureMiser applications manual. This information makes the consulting engineers task of specifying the MoistureMiser an easy one. The packaged rooftop and its de-humidification equipment are already designed and integrated together as one system. This will save the consulting engineers valuable time and allow them to specify and bid their jobs at a quicker and less complicated rate.

Another advantage the MoistureMiser provides for the engineer, as with the contractor, is that it is delivered factory installed by Carrier. One company handles all application support, service, and warranty issues. The consulting engineer only has to deal with one company.



Throughout this case study, the innovative design of the MoistureMiser has proven to give the building owner flexibility in the control of his space temperature and humidity. These units can be controlled to maximize the sensible or latent capacity based on the demands of the space conditions. As proven in this case study, the MoistureMiser package reduces the moisture content of the space by over 15%, made employees and customers feel more comfortable, reduced utility costs by 7%, and decreased compressor run time by 20%. It has also proven to be a cost effective alternative to the Heat Pipe. These facts make the MoistureMiser's performance the ideal weapon for humidity control in the small rooftop market. This test confirms that in areas of high humidity, both inside and out, a MoistureMiser option should always be considered due to the great benefits it provides. As proven by Sam Risola, "We are very pleased with this test and we have other units we are planning on replacing with the MoistureMiser."

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