Control Systems Info

Cube Refrigeration Control Systems

 

General

 

The cube has been designed to generate accurate refrigerated food storage temperatures by us-ing a food substitute contained within an enclosure to allow a microprocessor temperature sens-ing probe to be contained within a food grade food substitute with variable size cable termina-tion to fit modern refrigeration controls, treat without changing the manufacturers specification, link i.e. to be fitted to the sensor inside the evaporator in the refrigerated return air. At normal manufac-turer’s procedure, search once in place, contained within the enclosed evaporator no further attention would be needed.

 

The advantage of food monitoring based on food temperatures and not air is now becoming an accepted principle of refrigerated storage, which we have pioneered and refined through exten-sive research and field trials into a viable retrofit product, to enable accurate monitoring via wireless transmission generating high temperature alarms, etc.

 

Energy Saving Advantages of the Cube

 

By using the cube as a device to control food storage temperatures, a more efficient refrigera-tion cycle is attained. At the moment air cycles (on/off) typically produce a minimum of 12 cy-cles per hour, and in some open display cases 20 cycles per hour. By using the cube as a cycle control mechanism a reduction of refrigerated cycles can be lowered by as much as 80%. (Example: Dairy Case: air cycles 3 minutes on, 2 minutes off = 12 cycles per hour. With the cube fitted it changes its cycles to 8 minutes on and 7 minutes off = 4 cycles per hour. This ex-ample equates to a 66% reduction in starts).

 

As the start up of a refrigerator compressor uses 3 times more power (i.e. start up amp is 12 amps, run amps is 4 amps) this will result in a power consumption reduction of 16% to 22%. (See research results and test procedures)

 

1. Reasons for the benefit of longer on cycles on the food

2. Advantages of longer off cycle.

3. Lower temperatures achieved without heat induced defrost cycles

4. Reduction of noise nuisance on remote (situated on the outside of the building) condens-ing units.

5. Advantages of using the cube in relation to the off cycle, as opposed to pump down off cycle, reducing energy consumption by a further 10%.

 

1. Reasons for the benefit of longer on cycles on the food

 

Normal air cycles will operate as the air temperature attains the set point of the thermostat. This will generate several on/off-cycles, without having very much effect on the food temperature. I.e. several 3 min on-cycles. However with cube fitted, this changes to 10 min on-cycles, result-ing in a positive food temperature reduction by cooling the food quicker, leading in turn to a safer food.

 

Thus installing the cube leads to a more efficient use of the refrigerator system combined with a lower energy consumption and safer food.

 

The longer on-cycle will create a higher efficiency of the refrigeration cycle i.e. longer runs at a maximum advantage (compare it to fuel consumption and efficiency in a car on a stop start ur-ban road, or a long stretch of motorway driving at a steady 70 miles an hour).

 

2. Advantages of longer off-cycles.

 

A longer off-cycle will allow a pressure equalisation between the high and low pressure parts of the refrigerant within the refrigeration system, allowing a softer start from a cooler system, thus avoiding compressor trip caused by high pressure or an unbalanced system. I.e. lower amperage clean start obtains a maximum efficiency far quicker (with a further energy saving).

 

The electrical starting component and devices used on refrigeration equipment have an engineered life span, so the less maximum power use of these components will extend the reliability of the components, reducing refrigeration failure pro-rata. Thus using cube technology will ex-tend the life of the starting devices and in turn the refrigeration equipment, with fewer break-downs and engineer call outs.

 

3. Lower temperatures achieved without heat induced defrost cycles

 

Due to the low evaporating temperatures of refrigerants, to maintain a refrigerating temperature within a refrigerated space, the evaporator temperature will have to be below freezing (i.e. chill-ers evaporating temp -10deg C to maintain a storage temp of +4deg C, and freezer evaporating temp -30degC to maintain a temp of -20deg C). In all cases a frost will form on all evaporating surfaces.

 

We will deal with fresh meat temperature storage (-1 to +1 deg C) to highlight the advantages of natural defrost for fish keepers, seafood storage and fresh meat conditioning (hanging) by using the cube as against heat introduced defrost which is presently the only way to achieve defrost.

 

As already established evaporating temperatures are at least 10 deg C below storage temperatures thus creating frost on the evaporator surfaces (fins), so a periodical application of heat has to be applied to the evaporator surfaces to melt the frost to condensation. This is done by preset defrost intervals, applying heat by electric heater or reverse cycle hot gas defrost. i.e. 4 defrost per 24 hr period at 20 min duration; terminate by termination klixon or thermostat. The intro-duction of this heat has to be removed after the termination of the defrost cycle, when the re-frigeration cycle is re-instated. This format produces heat that has to be removed from within the refrigerated space (fridge). The conclusion is that heat is introduced into the defrost cycle, which the refrigeration cycle has then to remove to return to set refrigeration storage tempera-tures, a process which is, to say the least, very uneconomical.

 

The installation of the cube with the advantage of longer on-cycle and extended off-cycle will allow temperatures to rise just above freezing to allow the evaporator frost to blow clear with-out the introduction of enforced heat (as no frost has then to be removed this leads to a large reduction in the use of enforced defrost heaters with a subsequent reduction in energy usage), so a natural defrost cycle on the normal off-cycle by use of the cube allows safe fresh meat and

 

4. Reduction of noise nuisance on remote (situated on the outside of the building) condensing units.

 

The following points deal with noise nuisance from commercial establishments in high density rural and urban areas, generated by remote refrigeration equipment sited outside the premises, i.e., refrigeration and air-conditioning condensing units mounted outside of commercial prem-ises: i.e. convenience stores, restaurants, hotels, etc.

 

As has been described previously the reduction of refrigeration cycles provide closer and more efficient food storage and energy saving. A further advantage in fewer starts is a great reduction in the noise pollution caused when refrigeration and air-conditioning condensers are located outside commercial premises. The stopping and starting of refrigeration equipment can cause great annoyance in areas where commercial premises are mixed with residential dwellings. It is apparent that a softer and quieter start up reduced from 12 to 20 starts per hour to perhaps 4 per hour will ease this situation. The cube can also be used to initiate off-time during sensitive hours, tailored to fit in with reasonable requests.

 

5. Advantages of using the cube in relation to the off cycle, as opposed to pump down off cycle, reducing energy consumption by a further 10%.

 

It has long been accepted practice for larger commercial refrigeration equipment i.e. coldrooms, display cases, etc. to use a pump-down defrost cycle. The pump-down defrost cycle will only apply to equipment designed for lower temperature ranges i.e. freezer coldstores -18 to -22 deg C and fresh meat, poultry or fish etc. -1 to +1 deg C.

 

Typical defrost periods are 4 x 24 hours at approximately 20 minutes duration, these settings are adjustable to accommodate variable sitting and conditions.

 

This pump-down application is necessary during defrost, when heat has to be applied to the evaporator surfaces via a system of heaters (electric element) to remove any frost build up on the evaporator surfaces. The pump-down is to remove the refrigerant from within the evaporator coils, because the introduction of heat will cause expansion of the refrigerant throughout the system, causing very high back pressures when the compressor is re-started on the termination of the defrost.

 

The pump-down procedure is as follows: when a defrost is initiated via a time clock or micro-processor, the electrical supply to a magnetic flow valve in the liquid refrigerant delivery time is interrupted, closing the valve. The liquid refrigerant is pumped into the high pressure side of the system drawing all refrigerant from the low side of the system (evaporator suction line), this pumping action is completed by the compressor when the low pressure is reduced to approximately 1lb psig (per square inch gauge pressure), and the condensing unit will stop via a low pressure switch. At this point the refrigerant has been pumped to the high pressure side of the system, where it will remain for the preset period of the defrost. At the termination of the defrost, power will be restored to the magnetic valve, the refrigerant will then flow through the system activating the low pressure switch as the pressure rises, initiating the start up of the condensing unit. This will run for a short time without the Evaporator air circulation fans, to allow the evaporating surfaces to cool down to a preset temperature before air-circulation can be re-stored.

 

This fan delay is in place to prevent the circulation of warm air within the refrigerated space.

 

It has to be noted that on commencement of pump-down defrost, a small amount of refrigerant will remain on the low side of the system so that when the heaters are on this small amount of refrigerant will expand, increasing the pressure switch as the pressure rises. This will start the condensing unit for a few seconds (up to 60 seconds) to keep the pressure on the low-side at 1lb psig. This procedure is likely to happen several times during the defrost cycle. This very short run time is important, as it is relevant in the next part of this paper.

 

Misuse of pump-down for remote condensing units.

 

Remote condensing units are best practice on commercial equipment. A simple explanation is when coldstore display cases are sited within a building or premises and the condensing units are situated in weatherproof housing outside the building, the inside and outside being interconnected with pipe work, electric cables and drains (for condensate water). This method is used to attain better heat transfer i.e. removal of heat from within the refrigerated space inside the building, then dissipated to air via the refrigerated cycle outside the premises.

 

This is the ideal efficiency as far as heat removal is concerned, but far from ideal when it comes to noise nuisance, especially in sensitive urban areas, i.e. if a convenience store has an average of 4 to 6 remote condensing units at the back of the building outside in the back yard, the constant off/on (24 hours per day) of this equipment can cause much conflict in a neighbourhood, especially at night in the summer when people sleep with the windows open!

 

This brings us to our observations of poor refrigeration practice, noise pollution and excessive waste of electricity.

 

A refrigeration condensing unit will run for a period of time (i.e. 3 minutes) to reduce the temperature within the refrigerated space. When the set temperature is achieved the unit will cut out until the temperature rises to a preset differential (i.e. +/- 4degC). This will take approximately 2 to 3 minutes, thus producing approximately 12 stop/starts per hour. It is at this stop/start cycle that the machinery is at its most voluminous. As an example, if a Spar shop or equivalent has six condensing units outside the building this will produce 72 stop/starts per hour. A lot of noise nuisance!

 

A further reason for highlighting this off-cycle pump-down is that in common with pump-down defrost, some refrigerant remains within the evaporator, so that natural heat gain (without heaters, this is not defrost) will expand the remaining refrigerant, causing the condensing unit to start up 2 or 3 times for a few seconds on each off-cycle. This will produce 36 to 48 starts per hour. If the pump-down off-cycle was changed to a normal straight stop cycle using a cube, the no. of cycles will be reduced from 36-48 per hour to 3-4 per hour. Estimated saving on power consumption is approximately 40%, not to mention the significant wear and tear on the compressor and starting devices.

 

We have observed that the pump-down off-cycle causes the system to stop and start in an un-balanced pressure state on the stop, where the pressure will be 100 to 200 psig. The pressure on the low side will be reduced to the set point of the pressure switch

 

(L.P. switch) of approximately 1lb psig, this causes high noise values where a very audible bang can be heard from within the compressor. Most compressors are hermetically sealed with crank-shaft pistons, valves and electric motor suspended on mounting springs. It is obvious that due to the sudden shock of an equalised start up; the mounting springs are stretched, causing high level vibration. In extreme circumstances the springs can break away from the suspension mounting, or fracture the discharge pipes inside and/or outside of the compressor, causing total refrigeration failure and external leakage of refrigerant, with its well documented harmful effects on the environment.

 

To compound this problem, pump-down off-cycle (not defrost) has become standard practice in the last 10 years or so.

 

The above problems are now resolved by the use of a cube as a control, which will reduce stop/start cycles from approximately 12 starts per hour to approximately 3 to 4 starts per hour, thus reducing noise and producing energy saving of approximately 20% plus. I.e. a dairy display without a cube will generate 1 complete cycle every 5 minutes producing 12 cycles. With the cube fitted, this changes to 1 cycle every 15 minutes, producing 4 starts per hour. Harry – I assume that here we should also mention that the cube will make sure that the system, when fitted with a cube, will start in a balanced pressure state, so that the sudden shock to the system leading to the typical problems that this can cause. Is alleviated, and the audible bang is not caused.

 

We have many examples of successful usage of cube technology for noise reduction, energy saving and more accurate food storage temperatures.

 

Conclusions

 

 

  • The cube is a retrofit product, one operation with no further attention required afterwards, nor any maintenance.
  • The cube can be fitted within the evaporation space which would be inaccessible to unqualified personnel.
  • The cube creates accurate food temperature monitoring via radio transmission and visual LCD display.
  • The cube can be fitted to sensor at the manufacturing stage, making the two parts a single product.
  • The cube enhances refrigeration efficiency by initiating a longer on-cycle culminating in a longer off-cycle, inducing a natural off-cycle defrost for chillers (-1 to +1degC) (+1 to +5degC). It should be noted that the initiation of natural off-cycle defrost enhances efficiency by keeping evaporation surfaces clear of frost, allowing only a small frost build up. Frost restricts air-flow through evaporator surfaces, and also acts as a partial insulation against good heat transfer, so that relying on a heat induced defrost at 6 hour intervals is run on a frosted coil (evaporator) reducing efficiency.
  • Reduction of energy and reduction of noise nuisance have been dealt with at length in previous paragraphs.
  • The cube will provide safer food, energy saving, increased machinery life, reduction in environmental pollution and less product spoilage.