building science.com © 2008 Building Science Press All rights of reproduction in any form reserved. Advanced Space Conditioning Building America Report - 0007 2000 Joseph Lstiburek Abstract: Everything you ever wanted to know about HVAC for homes-thermal comfort, air distribution, nature of and dealing with contaminants, HVAC strategies, and climate-appropriate graphics to boot. RR-0007: Advanced Space Conditioning Advanced Space Conditioning © buildingscience.com Design Trade-offs and Test Plan for High Performance Space Conditioning Systems Advanced Space Conditioning 2 Table of Contents Introduction ................................................................................................................................ 4 Advanced Space Conditioning ....................................................................................................... 4 Background ................................................................................................................................ 5 Thermal Comfort ................................................................................................................ 5 Outside Air Supply ............................................................................................................. 6 Building Envelope Leakage ................................................................................................ 7 Controlled Ventilation......................................................................................................... 8 Air Pressure Control ........................................................................................................... 9 Control of Pollutants......................................................................................................... 10 Combustion Products ............................................................................................ 11 Mircrobial Contaminants ...................................................................................... 11 Radon .................................................................................................................... 12 Formaldehyde and Other Volatile Organic Compounds ....................................... 12 Synthetic, Natural and Benign Materials.............................................................. 13 Particulates............................................................................................................ 14 Heavy Metals ........................................................................................................ 15 Ventilation .............................................................................................................................. 16 Cold Climates ...................................................................................................................16 Hot-Humid Climates ........................................................................................................ 17 Air Distribution............................................................................................................................. 19 High Performance Glazing ............................................................................................... 19 High Levels of Insulation ................................................................................................. 20 Low Building Envelope Leakage ..................................................................................... 21 Distribution System and Building Envelope Integration .................................................. 21 Return Paths...................................................................................................................... 25 Heating and Cooling Equipment .................................................................................................. 25 Water Heaters .............................................................................................................................. 28 Examples of Advanced Space Conditioning ................................................................................ 28 Appendix A: Building America Metrics ....................................................................................... 30 Appendix B: Example of Advanced Space Conditioning Systems .............................................. 33 3 Advanced Space Conditioning Introduction Advanced Space Conditioning High performance building envelopes Advanced space conditioning involves the require controlled ventilation systems, sealed integration of a building’s heating, ventilating combustion appliances and allow the use of and air conditioning (HVAC) system with the innovative air distribution systems. building enclosure or building envelope. This The optimum controlled ventilation system integration is dependent on the characteristics of in all climate zones is a supply ventilation the building envelope. High performance build- system that allows for filtration of outside supply ing envelopes have very different requirements air and the pressurization of building enclosures for HVAC systems than standard building enve- to exclude environmental contaminants. lopes. High performance building envelopes also provide opportunities for HVAC systems that are In very cold climates, this supply ventila- not available with standard building envelopes. tion system is coupled with a high performance building envelope that has a high drying poten- The following discussion pertains to high tial to compensate for the pressurization effects performance building envelopes. A high perfor- of the ventilation system. mance building envelope is defined as a building envelope that meets both the EnergyStar thermal In hot-humid climates, this supply ventila- requirements and the air tightness requirements tion system is coupled with supplemental dehu- of the Energy Efficient Building Association midification in order to address part load issues. (EEBA). Additional requirements relate to rain In all climates, air distribution systems are control, ground water control, and water vapor located completely within the conditioned spaces control. The specific metrics defining high thereby minimizing the effects of duct leakage performance building envelopes are contained in and air handler leakage. Additionally, all air Appendix A. distribution systems are air pressure balanced to Advanced space conditioning involves prevent the pressurization or depressurization of HVAC system innovations in the following rooms. areas: The high performance aspects of the build- • ventilation ing envelopes allow for the simplification of duct distribution systems. Single returns replace • air distribution distributed returns. Supply registers no longer •heating equipment need to be located at building perimeters at •cooling equipment window locations. All ductwork is fully sealed •water heaters and “hard ducted”. No building cavities are used as returns. Each of these areas will be explored. In hot-humid climates and hot-dry climates the construction of unvented, conditioned attics allows for the installation of air handlers and ductwork above ceilings – but still within condi- tioned spaces. Advanced Space Conditioning 4 Background biological concentrations. The ultimate objective of a successful Heating, ventilating, and air conditioning environmental system is to provide for the (HVAC) systems involve both thermal comfort comfort and welfare of the occupants and pre- (the heating and air conditioning components) vent an accumulation of unpleasant and/or and dilution of interior pollutants (the ventilating harmful pollutants. component). The HVAC system includes all heating, cooling, and ventilation equipment Occupant comfort complaints constitute a serving a building including their associated significant portion of indoor environmental distribution systems. complaints. If occupants are uncomfortable, they will complain. Thermal comfort must be main- The five principle functions of a HVAC tained within a building in order to provide for system are as follows: an acceptable indoor environment. •maintain thermal comfort under operating Many variables interact to determine conditions whether occupants are comfortable. The Ameri- •provide fresh air to the “head space” of can Society of Heating, Refrigerating, and Air- occupants in sufficient quantity and quality to Conditioning Engineers (ASHRAE) Standard dilute pollutants generated by occupants, 55-1992: Thermal Environmental Conditions for furnishings and the structure (outdoor air Human Occupancy describe the temperature and supply and ventilation effectiveness) humidity ranges that are comfortable for most • facilitate source control of pollutants by people under various activities. Some of the providing adequate interzonal and interstitial variables discussed in Standard 55-1992 are: pressure control (system operation, mainte- • uniformity of temperature (temperature nance, commissioning/balancing) stratification, convection) • facilitate source control of pollutants by • radiant heat transfer (cold or warm surfaces providing “capture at source” exhaust ventila- such as windows) tion at pollutant generation locations and • relative humidity preventing reintrainment of this exhaust ventilation (local exhaust) • activity level, age and physiology of occu- pants • facilitate source control of pollutants by providing air cleaning (filtration of particles, • clothing levels gases and dehumidification of airborne mois- There is considerable debate