CPD Programme CPD Programme
The CIBSE Journal CPD Programme Members of the Chartered Institution of Building Services Engineers (CIBSE) and other professional bodies are required to maintain their professional competence throughout their careers. Continuing professional development (CPD) means the systematic maintenance, improvement and broadening of your knowledge and skills, and is therefore a long-term commitment to enhancing your competence. CPD is a requirement of both CIBSE and the Register of the Engineering Council (UK). CIBSE Journal is pleased to offer this module in its CPD programme. The
programme is free and can be used by any reader. It is organised jointly by CIBSE Journal and London South Bank University, and will help you to meet CIBSE’s requirement for CPD. It will equally assist members of other institutions, who should record CPD activities in accordance with their institution’s guidance. Simply study the module and complete the
questionnaire on the final page, following the instructions for its submission. Modules will remain available online at
www.cibsejournal. com/cpd while the information they contain remains current. You can also undertake the questionnaire online, and receive your results by return email.
Evaporative cooling enhancement on air cooled chillers
How can evaporative cooling deliver improved performance, and what are the cost implications? These are some of the issues examined in this month’s article, which follows up a previous CPD on chillers
air intake to the condensers. The theory of evaporative cooling will be presented, together with the improved performance data and an application into modular data centre air conditioning packages. This follows on from the CPD article in
T
the July 2009 Journal, which introduced several innovative improvements to the performance of centrifugal compressor water chillers. These included: • Magnetic bearings within the compressor; • Oil free compressor; • Floating head pressure; • Micro-channel aluminium condensers, that reduce refrigerant charge while increasing the effectiveness of heat exchange; • Flooded evaporators that ensure optimum energy transfer between refrigerant and water; • Inverter-controlled compressors whose
www.cibsejournal.com
his month’s article features a further improvement to the performance of air cooled chillers in the form of evaporatively cooling the fresh
output can be matched to the load; and • Use of a liquid refrigerant pump system that significantly increases thermodynamic efficiency across the chiller’s operating range.
Evaporative cooling systems Evaporative cooling is achieved with a cassette made from inorganic, non-combustible packing material, which is a resin coated board – one that is fireproof and will not support bacterial growth. Figure 1 shows the typical air cooled chiller arrangement. The cassettes are set in front of the V bank epoxy coated condenser coils and can be slid out for replacement or winter operation to reduce fan pressure drop. The system incorporates a once-through
water system with micro jet spray nozzles, which means that only the minimum amount of water is used with the water being pumped by a variable speed drive pump, through a UV filter to kill all bacteria. The sprayed water flows onto the corrugated
surface of the cassette material and saturates the material, but without passing through and coming into contact with the condenser coils. As the warm, dry ambient air passes
through the cassette it evaporates a proportion of the water, lowering the air dry bulb temperature and raising the humidity. The fans are variable speed drive with electronically controlled motors to reduce energy usage. Approach temperatures between refrigerant condensing temperature and air onto the coils are reduced by up to 8K at peak design conditions (35C ambient). Condensing temperatures are reduced and condenser fan volumes also lowered, so energy savings can be very significant. Utilising the flow/power cube law, savings of up to 30% are possible. The evaporative unit can be automatically
switched off at lower ambient conditions, when water cost equals or is greater than potential energy savings. Excess water assists in washing the media, and is drained back
July 2010 CIBSE Journal
> 55
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68