. Level 3 Air Conditioning Inspections for Buildings 14. Efficiency of Air Conditioning Systems (Day 3) PRESENTED BY Anthony Balaam aircon@stroma.com

The Refrigeration Load Cooling Load The Refrigeration Load Cooling load on a refrigeration system determines:- 1. The plant size 2. and the power consumption This does not effect the Coefficient of Performance (COP). No refrigeration load = no COP or efficiency The smaller the load, the lower the electricity power consumption.

Coefficient of System Performance (COSP) Efficiency of a Refrigeration Cycle The coefficient of system performance (COSP) is expressed as the capacity (kW) divided by the power input (kW) required to produce the cooling:- capacity (kW) power (kW) COSP = This takes into account all fans, motors and controls associated with the system. The Seasonal Energy Efficiency Ratio (SEER) is now commonly used as it takes into account the seasonal performance.

Coefficent of Performance Efficiency of a Refrigeration Cycle The coefficient of performance (COPc) is expressed as the useful cooling duty (kW) divided by the power input (kW) required to produce the cooling: The maximum efficiency, ‘Carnot cycle coefficient of performance’, is based upon a theoretical thermodynamic cycle on which the actual cycle is based: COPc = Te/(Tc-Te) Where:- Tc is the condensing temperature (K) Te is the evaporating temperature (K) ‘c’ denotes a cooling COP This does not take into account of all fans, motors and controls associated with the system, compressor only.

Efficiency of a Refrigeration Cycle Performance Efficiency of a Refrigeration Cycle An actual COP would be typically 50% less than the theoretical COP due to:- 1. Deviations from the theoretical cycle 2. Inefficiencies within the practical cycle like:- A. Pressure losses B. Heat transfers Example: A COP of 3.7 means… The refrigeration unit will produce 3.7kW of cooling per kW of electrical consumption by the compressor motor. Question: Why is the efficiency greater than 1? Surely this is against the laws of thermodynamics…?

Efficiency of a Refrigeration Cycle Performance Efficiency of a Refrigeration Cycle Answer:- Cooling duty is in kW of heat exchange energy, whereas the power input is electrical or work done energy. If: power input was expressed as heat energy (i.e. considering the energy used to produce the electricity), then the ratio would be less than 1 (or… 100%). COP provides useful information about the running costs of the refrigeration system with respect to the cooling duty.

Answer COP = Cooling Output (kW) / Power Input (kW) 3.7kW Heat Rejected Atmosphere COP = Cooling Output (kW) / Power Input (kW) COP = 3.7kW / 1kW = 3.7 1kW Electrical Power 70% Losses 3.7kW Heat Absorbed Occupied Zone 2.5 kW Fuel

Efficiency of a Refrigeration Cycle Performance Efficiency of a Refrigeration Cycle COP is most dependant on temperature difference (or temperature lift) between the condensing and evaporating temperatures. Smaller the difference, greater the COP Bigger the difference, lower the COP You will get around 2-4% increase in performance for:- 1. 1K increase in evaporating temperature 2. 1K decrease in condensing temperature COP is also affected by:- Refrigerant type Equipment used Controls and maintenance

1. Raising the Evaporating Temperature COP Factors 1. Raising the Evaporating Temperature To achieve this use an evaporator with a higher basic rating is used (usually a larger evaporator). The evaporator is defrosted if necessary. Also ensure the evaporator is clean and free of blockage.

2. Lowering the Condensing Temperature COP Factors 2. Lowering the Condensing Temperature To achieve this - Use a condenser with a high basic rating (usually a larger condenser). Allow the condensing temperature to float down with the ambient temperature. Average UK temp is around10˚C, this should be used to advantage, as opposed to holding a condensing temperature artificially high. Can save in excess of around 25% energy. Use water instead of air as condenser medium. Also - Ensure condensers do not become blocked, or flow of cooling air or water becomes impeded in any other way.

Compressor Efficiency COP Factors Compressor Efficiency Varies with type and manufacturer. The most efficient compressor for an application, should be selected. This depends on:- 1. Size of cooling load. 2. Refrigerant used. 3. Temperature of the application. 4. The average temperature of the cooling medium (air/ water)

COP Factors Amount of Refrigerant This has a significant effect on the temperature lift. Too much or too little, reduces efficiency. Systems that leak refrigerant consume more power than necessary. Costs UK refrigerant plant owners an extra 11% per year. Over charged systems have more refrigerant to lose in the event of a leak which is environmentally detrimental.

COP Factors Refrigerant Type Variation of this can effect the COP by up to around 10%. Hardware needs to be optimised to the refrigerant for benefit. The most efficient refrigerant for an application depends upon:- 1. Compressor type 2. Temperature of the application 3. Average temperature of the cooling medium (air/ water).

Superheat of the Suction Vapour COP Factors Superheat of the Suction Vapour This needs to be as low as possible. Warmer vapour reduces the capacity of the compressor; Also, it does not reduce its power input. On direct expansion systems it is achieved by:- 1. Correctly controlling the expansion device; 2. Insulating the suction line.

COP Factors Amount of Sub-cooling This should be as high as possible. By Increases the capacity of the system. But does not increase its power input. The Liquid line should not:- 1. Should not be insulated. Should not pass through any hot areas (like kitchens, direct sunlight).

Usage in building services Comparison Cooling method Usage in building services Efficiency Capital cost Carbon footprint Vapour compression High Low Medium Absorption: Generated heat Waste/free energy Air cycle Evaporative Dessicant Carbon dioxide Evaporative and dessicant cooling are often used in conjunction with vapour compression or absorption, as they can only produce cooling temperatures down to about 15 °C. Absorption cooling using free thermal energy such as solar power will have almost infinite efficiency and zero carbon footprint, but if absorption systems are gas or hot water driven, their efficiency will be low and their carbon footprint high. (See section 6 for more information on absorption cooling.) Carbon dioxide is being increasingly used in computer systems with the cooling built into the computer hardware. Air cycle cooling is still at the development stage for building services applications. There are other methods of cooling such as thermoelectric, magnetic, vortex, Stirling cycle etc, which have very limited application at present.

NDHCVCG Energy Efficiency Ratio (EER) Non-Domestic Heating, Cooling and Ventilation Compliance Guide (Second Tier Ref: ADL2B) For Cooling:- Energy Efficiency Ratio (EER) For Chillers; EER is defined as the ratio of cooling energy delivered, divided by the energy input to the cooling plant. For Packaged Air Conditioners; EER is defined as the ratio of energy removed from air within conditioned space, divided by the effective energy input to the unit

Seasonal Energy Efficiency Ratio (SEER) Cooling Seasonal Energy Efficiency Ratio (SEER)

SEER Profile Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec A B COP100 COP75 A B C D Heating COP50 COP25 Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec EER25 EER50 Cooling EER75 EER100

Cooling Energy Efficincy Ratio (EER)

Cooling Cooling Controls:-

Cooling Determining The SEER - no part load data

Cooling Determining The SEER – by part load data

Reference Material “Heating, Ventilation, Air Conditioning and Refrigeration”, CIBSE Guide B, Chartered Institute of Building Services Engineers, 2005 “CIBSE KS13: Refrigeration”, CIBSE Knowledge Series, Chartered Institute of Building Services Engineers, 2008 “ASHRAE Handbook: Fundamentals”, American Society of Heating, Refrigeration and Air Conditioning Engineers, 2001 “BS EN 378: Specification for Refrigeration Systems and Heat Pumps; Part 1: 2000: Basic Requirements, Definitions, Classification and Selection Criteria; Part 2: 2000: Design, Construction, Testing, Marking, and Documentation; Part 3: 2000: Installation Site and Personal Protection; Part 4: 2000: Operation, Maintenance, Repair and Recovery”, London: British Standard Institution, 2000 “Non-Domestic Heating, Cooling, and Ventilation Compliance Guide”, Department For communities and local Government Building Regulations Approved Document L2B”, Department For communities and local Government

LEVEL 3 Air Conditioning ENERGY ASSESSORS TRAINING ANY QUESTIONS OR FEEDBACK ON ANY SLIDE Any questions or clarity needed over this topic and slides 25

Contacts:- STROMA Certification Ltd – Contacts Web Links www.stroma.com/certification Contacts:- STROMA Certification Ltd. 4 Pioneer Way, Castleford, WF10 5QU 0845 621 11 11 training@stroma.com

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