Chillers offering heat reclaim facilities are a welcome development but it is important to establish the heating need for the system to work efficiently, says Roger Palamarczuk of Ferroli dpac UK.
THE basic concept of commercial water chillers has not changed dramatically over the years.

The components to drive the system have benefited from material and engineering developments which have increased the efficiency of the package. Environmental concerns have pushed the development of new refrigerants and the overall efficiency levels have increased.

Heat reclaim is an exciting addition and should be incorporated wherever possible. Saying that, it is important to recognise there must be a need for heating for the system to work. Don't generate hot water or warm air if you don't have to.

Air-cooled systems form the majority of chillers sold into the UK and special versions have been developed to achieve the utmost in energy savings. Ferroli has developed a step-by-step approach to the design of each version of water chiller and heat pump chiller so the designer can select the most appropriate product.

Here we look at the efficiency levels published and ratified by an independent laboratory. For comparison purposes typical design conditions and capacity range have been selected as follows:

Chilled water temp: inlet 12°C, outlet 7°C
Ambient temperature: 35°C
Recovery water temp: inlet 40°C, outlet 45°C
Evaporator fouling factor: 0.44x10-4 m2 ºC/W
Recovery fouling factor: 0.88x10-4m2 ºC/W
Refrigerant: R134A

The Ferroli RHV has a capacity range of 330kW to 1400kW and we have taken the average efficiencies with the appropriate noise pollution levels, both of which will have an effect on the environment.

Ferroli RVH air-cooled water chillers with helical fans


EER SEER SWL SPL

(dBA) (dBA)
RVH Basic 2.8 3.73 100 73
RVH AS Low Noise 2.66 3.66 95 67
RVH ASS Extra Low Noise2.55 3.56 90 62

Every chiller is attached to a building that will have a need for potable hot water if not space heating or even process hot water. This is achieved by incorporating a refrigerant to water heat exchanger into the discharge of the compressor before the condenser coil. A diverting valve will direct the superheated refrigerant to the appropriate heat exchanger, and allow a degree of recovery. The recovered heat can be stored for use when required. This will amount to approx 30% of the cooling capacity at design conditions, and we can expect the low noise versions to better this by approximately 3% for each version.

In perspective, there is 152kW of recoverable heat on a 511kW capacity chiller. There will be diversity for seasonal and occupational variation, but thermal storage systems will make that heat capacity available almost the whole year.

There is an additional option to increase the leaving hot water temperature to 50°C, and in some of the smaller ranges it can exceed 60°C. Now we are in the realms of making the conventional boiler redundant.

Ferroli RVH 510.2 air cooled water chillers with helical fans and desuperheater

Cooling capacity Recovered heat

(kW) (kW)
RVH Basic 511 152

Ferroli RVH 510.2 air -cooled water chillers with helical fans and total recovery

RVH Basic 511 680

If there is a greater need for hot water - a process plant that is continually washing down for example, then we can look at total heat reclaim. This would average out to be a staggering 130% of the refrigeration load. We do have the opportunity to inflate the leaving hot water temperature to 50°C, but this gives 125% heat output from the chiller.

It would be difficult to obtain the higher temperatures achievable with the desuperheater as we lose some high temperature heat from the compressor discharge within the refrigerant to water condenser. By incorporating two condensers in parallel we must make allowances in controlling the head pressure in the air cooled condenser. This is done automatically in the factory to ensure the machine runs to specification all the time.

The same principles can be used in water-cooled liquid chillers, recovering heat from the compressor discharge by diverting it to a secondary heat exchanger. The efficiency levels for water-cooled plant are marginally greater than air-cooled, as can be seen in the chart here:

Ferroli RVW water-cooled liquid chillers
EER COP SWL Recovered heat
RVH cooling only 4.73 4.25 98.5
RVH cooling only
with soundproofing 4.73 4.25 94%
RVH cooling
with desuperheater 4.73 4.25 19% 19%
RVH cooling
with total recovery 4.73 4.25 113% 113%

These values do not take into account the type of heat rejection plant that would be adopted. The choice is between a water cooling tower and dry air cooler. From an energy perspective the tower is more efficient and takes up less space. Whichever is chosen the energy cost must be factored into the above efficiency levels.

There is a third option for both air- and water-cooled plant, and that is low temperature glycol systems. There is a further choice of ethylene glycol and propylene glycol, the main difference can be seen in the correction factor table below.

Propylene glycol has a marginally better energy performance characteristic than ethylene, but again the choice has to be made against the application. There would be another set of correction factors for the evaporator side of the chiller.

Using glycol on the condenser side would tend to suggest cooling at low ambient conditions so anti-freeze protection is the requirement. Using glycol on the evaporator side would suggest a process application or an ice storage system which would warrant the low temperatures seen here.

Ferroli dpac UK
0845 257 6380