Heat Pump Design

Four Points Engineering and Design

Project Number 99.04

F. P. E. D. Design Team Members:

Ricardo

302-837-1438

315 Pencader Hall J

Newark, DE 19717

Andrew
302-834-3201

22 Sonnet Dr.

Newark, DE 19702

Scott Quirico-

302-368-4509

11 Lincoln Dr.

Newark, DE 19711

Brian Zigmond

302-456-1687

260 Elkton Rd., Apt. F-3

Newark, DE 19711

Sponsor:

Christopher Whalen, Whalen Co.

Dept T., P.O. Box 1390

Easton, MD 21601

410-822-9200, Whalen @ shore.intercom.net

Executive Summary

The problem as presented by The Whalen Company to FPED is in three parts: Eliminate standing water, draw air from both rooms being conditioned, and decrease operating noise level in the current vertical, water-source heat pump unit. Though the three subsystems of the solution may not interact totally with one another, none of them may interfere with each other or compromise performance of the unit. FPED's mission is to solve this three-part problem in the given eight and half month period as economically as possible through a redesign and retrofit of the current unit.

The current model of the vertical heat pump we are analyzing puts out a maximum of 300 cubic feet per meter (CFM). Through numerous discussions with our customers and the use of the SSD matrix, several important metrics were obtained. They were number of parts in the design, the percent change of the footprint, and the time to fabricate. The target values for the aforementioned metrics are 12 total additional parts, 0 percent change in footprint size, and 1 ½ hours of additional manufacturing time for the drain pan, and two-room ducting. The goal is to optimize the key metrics with respect to the customer wants.

The addition of insulation and isolation materials serves to eliminate as much mechanical vibration noise as possible, then "trap" whatever noise can not be eliminated. To drain water from the condenser coils, we will attach a channel to the edges of the coils that will guide the water to a flexible hose, which will in turn take it directly to the drain hole. In order to draw air from the second room, installing a duct through the cabinet above the compressor will allow flow from the second room as well as provide easy access through the current access panel for the heat pump unit itself. Thus the three partial concepts can be combined into one complete solution, in which none of the improvements interfere with one another.

Background

The Whalen Company is an HVAC manufacturing company in Easton, Maryland specializing in providing high-end, single package, commercial units to hotels, apartment complexes, and hospitals. The unit has the smallest footprint in the industry, a key selling point, and also boasts of a removable chassis for quick and easy maintenance and repair. The sponsor wants to eliminate standing water to decrease the chances of breeding various biological hazards in hospital facilities, such as legionelae and mosquitoes, in the condensate drain pans of its units. The Whalen Company also wants to improve two other areas of the heat pump unit, namely circulation in the two room units and sound supression.

The three subsystems of FPED's solution may not necessarily interact totally with one another, but none of them may interfere with each other or the performance of the unit. As a perfect example, the two-room air draw, if done incorrectly, could cause a multitude of problems in the unit. If the air draw grill is put in the wrong place, the overall performance of the unit could be affected by blocking the blower fan in the unit. For these reasons, the approach to the problem is then to define wants that pertain to all three parts, then divide along three separate paths to "attack" each one. By creating three partial concepts and then incorporating the three to obtain a final concept, a complete solution to the problem will be obtained.

Our customers drive the wants generated in the project. The main customer is our sponsor The Whalen Company. However, the sponsor can be broken down into several internal customers with different priorities, along with a group of external customers such as the consumers of the product. In order to account for the differences of each group and their relative importance, we ranked their wants. From these wants we derived metrics which enable us to measure the wants. A detailed listing of the project's customers, wants and metrics is located in Appendix I.

The constraints faced in the scope of the project are those regulations imposed by the American Refrigeration Institute (ARI) and the Underwriters Laboratories (UL), as well as physical geometric constraints imposed by The Whalen Company 's current package design. The specific geometric constraints include a metal bracket in the bottom of the drain pan and the physical size of the wall the unit fits into. At this point the boundaries for the design space are now set, the constraints are not tradable and must be met.

Concept Generation

In generating concepts to any problem, industry standards are used to obtain metrics and target values with which to measure the problem. System benchmarking attempts to see if a unit currently in production will solve the problem completely.

The Trane Company has a standard vertical, water source heat pump that utilizes flush-mounted, hinged panels for quality sound attenuation and adjustable risers to accommodate varying height constraints. In addition, the drain pan is removable for ease of maintenance. ClimateMaster's 816 Series Heat Pump has 45 return air/discharge air options. In addition, the 816 series has three return air panels options for optimum sound dissipation. The unit also has a removable chassis for easy maintenance. There are also sound baffles on the intakes where the air enters the fan unit to eliminate compressor noise. Here we see that other manufactures have attempted to quiet the unit, only one of our partial concept solutions.

Next, functional benchmarking was done to see if we can take specific items from other manufacturers, or completely different sources to satisfy our problem. In addition, we tapped our primary source, Whalen, to obtain information about how they attempted to deaden sound and achieve the two-room air draw. From our benchmarking, we looked at using neoprene pads to dampen vibrations between the unit and the floor. Whalen currently offers that as an extra option. With respect to the two-room draw section, since no one in the industry currently markets a unit that is capable of drawing air from a second room, FPED will have to use whatever "in house" concepts that are generated.

Through discussions with our customers, and summing the values of the SSD matrix (Appendix II), several metrics stood out as the most important. Namely, the number of parts in the design, the percent change of the footprint, and the time to fabricate. The target values for these metrics are 12 total additional parts, 0 percent change in footprint size and 1 ½ hours of additional manufacturing time for the drain pan, and two-room ducting.

A way to maintain the smallest footprint in the industry is to keep all return air ducting internal to the unit, along with any condensation removal systems. The sound attenuation will not require the addition of more cabinet space to the unit. Since the assembly process in itself is simple, keeping the number of extra parts and the number of added assembly steps to a minimum keeps the assembly short. Therefore, we wanted to obtain a drain pan that could be fabricated as part of either the cabinet or the condenser coil unit. In addition, the insulation for sound would have to be attached as a part of the cabinet. The return air ducting would also have to be attached to the cabinet, which in theory will add time to the assembly process with the number of parts again kept to a minimum.

After analyzing the heat pump unit and conversing with Whalen engineering, we realized that all condensation water would come from the condenser coils, the frame of which currently incorporates a not-so-effective drain pan of its own. Water falls from the condenser to this channel, then drips off its edges into the main drain pan of the unit. Given that, we generated the concept of attaching a modified, sloped pan to the coil to catch the water. It will then guide the water to one of the four drain hole locations in the drain pan via a rubber hose. This is particularly effective because the number of parts would be minimal since this could be fabricated along with the housing that holds the coils.

In examining the unit for all metal to metal contact, we identified two areas that could benefit from neoprene isolation. Specifically, the blower fan and its housing could be separated with the neoprene, and the metal brackets that hold the compressor/coil chassis unit could be isolated from the chassis. This idea could be applied to any other similar points that could be generating noise, however none were identified. Other sources of noise identified are compressor noise and fan operational noise, which we hope to "trap" within a section of the unit by thoroughly insulating the area.

In order to return air from the second room, we chose to run a duct through the unit from the back to the removable inner panel. This duct will be located in the open area below the discharge fan and above the compressor. A deflector panel will guide the air from the duct to the front of the condenser coils. The area will be at negative pressure with respect to the room at the rear of the unit, thus causing airflow through the duct.

FPED has decided to attack the tasks put before us as three separate entities. Therefore, there will be three different concepts to solve the total problem. Prior to the trip to The Whalen Company, an idea for a positive pitch drain pan that would direct the water to one of the four holes in the unit’s drain pan was developed based on the drawings delivered to the team. However, the drawings were inaccurate, and failed to show a critical bracket on which the chassis of the unit slides and provides stability. Ideas for the two-room draw that would change the footprint of the unit were also developed, but this was of course prior to our knowledge that the footprint was a extremely high ranking want. Please see AppendixII containing complete SSD for other metrics.

Concept Selection

To select the best design from the concepts we generated, each of the concepts was evaluated against the metrics for the problem. This evaluation will be discussed in three groups corresponding to the three parts of the problem, then a final solution will be presented.

Sound Attenuation

Diffusion Ducting - The first concept was the installation of to control the flow and expansion of the air through the unit. After speaking with experts on turbulent airflow (Dr. A. K. Prasad, of the UD faculty and G. J. Sestak, P.E. and senior ASHRAE advisor) we found that the air velocity within the unit is not high enough to be turbulent, so the problems associated with a boundary layer and turbulent eddies were not produced in the cabinet. Calculations can be found in Appendix III. Since the flowing air cannot be a significant source of noise, any sound reduction concepts based this design would be unmerited. For completeness, further analysis of this concept is really not necessary but was carried out. When compared to the second concept discussed below, this idea ranked poorly in many other metrics as well, such as cost and ease of fabrication and installation.

If the unit noise is not due to the flowing air, then it must be due to mechanical (motor and compressor) noise. The second concept is the addition of insulation and isolation materials to eliminate as much mechanical vibration noise as possible, then "trap" whatever noise cannot be eliminated. This idea fairs well when weighed against most metrics. The concept is based on an obvious, well understood, and easily verified principle that by isolating and separating moving parts that are in contact, the vibration noise generated will be reduced. As a worst case scenario, we are assuming that all points in the unit that could be generating mechanical noise are generating noise, so all such points will be insulated or isolated. The testing determined not only the change in decibel level for the whole unit, but for each of the points in consideration. Please see Appendix V for details on sound testing of the unit.

Thus, we are planning on isolating and insulating the unit and its constituent parts. This design ranked better in virtually every metric, including the important one of decibel level, and its disadvantages are minimized.

Drain Pan

The first concept for the drain pan is to introduce an insert in the base of the unit that would be sloped to guide the condensate water to the drain hole. The drain hole may be in any of four positions, depending on the building piping for the drain risers. Unfortunately, two rail brackets extend up from the current base drain pan to provide support for the compressor chassis, which severely complicated this idea (see AppendixIV). This complication causes this concept to yield very high values for the metrics of ease and cost of manufacturing and fabrication due to the drastic change in the manufacturing processes that are currently in use.

The second drain pan concept is to attach a channel to the edges of the cooling coil that will guide the water directly to the drain hole. When evaluated by the metrics, this concept faired about the same or slightly better than the first concept in all metrics. Based on the metrics this concept is better than the first because it is a simple attachment to the current unit that would require no major modifications to the manufacturing process. Moreover this attachment is easy to manufacture (see Appendix IV).

Numerous other concepts were discussed and quickly shot down due to complexity and potential problems with the electrical system of the unit, and so are not ranked in the appendix. They include providing a heating coil to evaporate the condensation and actually mounting a pump in the pan to remove the water. Both would not only introduce an entirely new load on the current electrical system in the unit, causing Whalen to change the size of the transformers that are currently used in the unit production, leading to potentially exorbitant costs. On top of this, it would create another system within the unit that needed UL approval. Thus, these two "active" removal systems were not seriously considered.

The concept that we have selected for the drain pan is that of attaching a channel to the unit that will guide any condensation directly to the drain hole. Here we are assuming that the only water in the drain pan comes from the cooling coils. Once the unit is tested we will be able to verify this assumption. This design ranked better than the sloped insert concept in every metric being used to measure this design.

2 Room Draw

The early concepts generated required that the footprint of the unit be made slightly larger to accommodate the necessary ducting. Upon learning that the footprint couldn't be enlarged, these designs proved to be unacceptable and were scrapped.

In order to achieve the desired circulation in the second room of the two-room unit, the unit will have to draw air from that second room. A return air grill in the second room will be located in the rear of the unit. The air drawn into it will then be ducted to the front of the unit where the main return grill is located to pass the air over the coils. This is the basic solution of the two-room draw problem that all concepts will have in common. The designs will differ in where and how the air is ducted to the front of the coil.

The first concept is to utilize the large space present in the bottom half of the cabinet above the compressor chassis and below the fan to run the ducting. The second concept is to run the duct below the compressor chassis. A third concept would be a hybrid combining the above concepts. Another still would be to run the ductwork through the area over the discharge fan and run the ducting down to the return area.

These concepts all differ in only a few metrics. Since there is no opening in the cabinet above the fan other than the small air return, putting the ducting in the top of the cabinet would make it hard to access for installation and maintenance. Putting the ducting in the bottom of the cabinet allows easy access through the panel for the heat pump unit itself. The difference between the two concepts with ducting at the bottom is due to the amount of space available in the unit. There is a much smaller area in which to run ducting under the compressor chassis of the unit than if the ducting was to go above it. The lower duct would require more bending, resulting in higher manufacturing and fabrication costs, and would still give less intake area than the duct over the compressor chassis. Thus, the concept of running the ducting above the compressor of the unit is the superior idea. The prime metric here, since none of these concepts involve changing the footprint, is the increase in circulation, or the return CFM rate from the second room, which is a direct correlation to the face area of the return duct. So, the duct idea that may produce the best area with the lowest cost of fabrication. The choice is the duct over the compressor chassis and under the discharge fan.