Air Conditioning Inspections for Buildings Assessing Equipment Sizing PRESENTED BY NIRAJ MISTRY aircon@stroma.com
Size V s Load Regulation 22 of EPB Regulations The inspection report must include an assessment of the air-conditioning efficiency and the sizing of the system compared to the cooling requirements of the building, and contain appropriate advice on possible improvements to the system, replacement of the system and alternatives.
Cooling Loads Overdesign and Oversizing Environmentally unacceptable Operation at part load, reduced efficiency Uneconomical Overall wasteful Undersizing Conditions required for thermal comfort will not be met.
Cooling Loads Ambient Design Temperatures Selection of design ambient temperatures affects cooling duty; obtained from established weather data. It is possible for cooling applications that: temp C determining the cooling load temp C sizing the cooling plant. E.g. a dry bulb temperature of 28 C may be used for cooling load calculations, but a temperature of 32 C taken for selecting air cooled condensing equipment. Not overestimation of cooling load enables operation at higher ambient (the plant will be marginally oversized).
Heat Gains Heat Gains Can Cycle From Zero to 100% The following contribute to the cooling load: Heat through walls, floors, roofs, doors, glazing. Heat from air changes from doors, windows, ventilation systems. Heat from solar radiation. Heat from people within occupied zones. Heat from lighting and other energy consuming equipment. Heat from fan and pump motors associated with the systems. (paid for twice!)
Cooling Design Admittance Design conditions Architectural layouts and elevations Building use data Internal heat gain (sensible and latent) Building air tightness Infiltration heat gain (sensible and latent) U-values Fabric heat gain (sensible) Fabric details Solar data Solar heat gain (sensible) Fresh air ventilation load (sensible and latent) Duct/fan heat gains Detailed calculations to reasonable accuracy. Pipework distribution system design Total room heat gain (sensible and latent) Room cooling emitter size Distribution pipework heat gains Sensible/total room ratio Psychrometrics Dehumidification load Part L compliance (post 2002) will limit oversizing to 15-20%. Central Cooling Load Cooling load diversities Plant selection limitations cause oversizing. MAXIMUM INSTANTANEOUS COOLING LOAD Chiller Selection Plant size ratio
Cooling Design Design Recommendations Literature: CIBSE Guide A: Environmental Design CIBSE TM37: Improved Design for Solar Shading Control CIBSE TM46: Energy Benchmarks BSRIA: Rules of Thumb - Guidelines for Building Services BSRIA/CIBSE: A Practical Guide to HVAC Building Services Calculations BSRIA/CIBSE: Illustrated Guide to Mechanical Building Services CIP database file (available from www.ndepcregister.com) Software: Hevacomp IES Design Builder TAS
Cooling Estimation What is Required: Estimate of current loads. Provides: Indication of whether system is of appropriate size. Indication of current state of building and system. Assists: Future maintenance, replacement or upgrading of the system.
Cooling Estimation Help to inform on: replacement by like-for-like; or whether smaller more efficient system will suffice. Will indicate: Specific and localised load Special cooling measures Identification of oversized plant Waste of energy and costly.
Packged Systems Rules of Thumb: For units up to 7m from windows: 100W/m 2 for up 25% glazing 160W/m 2 for up to 60% glazing For units beyond 7m from windows (internal areas): 75W/m 2 For larger areas (perimeters and internal areas) 110 W/m2 for 30% glazing
Packged Systems Rules of Thumb: Estimation Only! Does not account for orientation, windows details, shading details (external or internal), or site details (adjacent buildings, trees etc.). Significant factors should be noted.
Centralised Systems Design Guidance Literature: CIBSE Guide A: Environmental Design CIBSE TM37: Improved Design for Solar Shading Control CIBSE TM46: Energy Benchmarks BSRIA: Rules of Thumb - Guidelines for Building Services BSRIA/CIBSE: A Practical Guide to HVAC Building Services Calculations BSRIA/CIBSE: Illustrated Guide to Mechanical Building Services CIP database file (available from www.ndepcregister.com) Software: Hevacomp IES Design Builder TAS
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 Inspection of Air Conditioning Systems, CIBSE TM44:2007