BUILDING AIR CONDITIONING
ZONING Components- Air Handler- controls air quantity, temperature, humidity, and quality (filters & circulates the air). Supply Duct- distributes conditioned air to outlets. Return Air- brings air back to the air handler (often in a plenum). Exhaust Air- sends contaminated air to the outdoors. Fresh Air- supplies outdoor air to replenish system.
ZONING COMPONENTS 1. Air Handler, 2. Supply Duct, 3. Return Air Duct,
4. Exhaust Air, 5. Fresh Air
ZONING ALTERNATIVES Zoning alternates provide methods for meeting various room differences /needs. Four zoning alternates are used: 1. Individual units 2. Single-zone installations 3. Zoned installations 4. Multizone installations
INDIVIDUAL UNITS Packaged units like window units or through-wall units that can heat or cool a room/area. Examples include heat pumps and AC units w/electric strip heat. Fan coil units that have hot & cold water piped to them. This will require central plants that have boilers and chillers as well as the piping runs to the fan coil units.
THROUGH WALL UNIT
FAN COIL UNIT
SINGLE ZONE INSTALLATIONS
Provides the same air to a large area or group of rooms. This requires that the rooms all have approximately the same needs for heating/cooling at the same time.
SINGLE ZONE INSTALLATION
ZONED INSTALLATION More than one air handler is used. Areas w/ like needs/requirements are served by the same air handler. Can have one air handler serving one area or you may have one air handler serving several areas.
Multizone equipment can provide air with different temperatures to different rooms/zones. Three types of multizone equipment are used: 1. Reheat- ducts cool air to a reheat terminal where a thermostat controls the reheating. 2. Double Duct- have separate warm & cool air ducts that both deliver air to a mixing box where a thermostat adjust the quantities of warm & cool air that are mixed. 3. Individual Duct- separate ducts to each room from the air handler with a thermostat controlling dampers in the air handler to proportion warm & cool air.
MULTIZONE INDIVIDUAL DUCT INSTALLATIONS
Air handlers can be equipped with mixing type heating and cooling coils where each coil may be operating to get a mix of warm and cool air. This is not the most efficient situation. Air handlers can also be equipped with bypass type configurations that allow for a flow of return air and either heating or cooling from the coils; whichever is needed to get the desired temperature.
VAV (Variable Air Volume) or CV (Constant Volume) Fans
The volume and temperature of the air that is available at the end of the primary ductwork and then flows into the secondary ductwork and out the diffusers can be controlled by the air handler (constant fan speed and variable temperature). VAV installations use a air handler with a variable speed fan and boxes at the ends of the primary ductwork to control the flow of air.
Variable Air Volume Fans (VAV)
VAV Terminal Box
VAV Terminal Box
VAV- Pros & Cons Pros: VAV installations can reduce fan operating cost compared to CV systems. Constant volume systems may have fans that run 24/7 which adds significantly to energy costs. Cons: Lower air flow may create poor air movement, a build-up of odors and higher humidity (comfort control problems).
SELECTING HVAC EQUIPMENT
Four Areas of Concern: 1. Heating- alternatives incl. heat pumps, furnaces and boilers. 2. Cooling- alternatives incl. heat pumps, air conditioners (air cooled condensers) & chillers. 3. Zoning- alternatives incl. individual units, single zone or multizone equipment. 4. Efficiency- must consider the building construction and the type of facility. Also consider any special circumstances (waste heat), initial costs and operating costs.
RETAIL BUILDING- CASE STUDY
Interior- single large space. Design considerations: 1. Low initial cost 2. Low operating cost 3. Low equipment maintenance 4. Store will stay in operation w/ a HVAC failure
HEATING SELECTION Use gas fired furnaces or if weather is mild, heat pumps. Use multiple units to allow for partial heating in case of one unit failing. Contract with local heat & air company that is the dealer for the equipment used and that maintains a large supply of replacement parts.
COOLING SELECTION Gas heating (furnaces) will work best with air cooled condensing units. Consider heat pumps in both packaged units and split systems. Consider location of condensing units for split systems- noise and refrigerant piping runs. Roof mounted equipment can save space and operate efficiently.
ZONING For the single large retail space a single zone, constant volume system will have lower first cost and will still perform well. Select programmable thermostats to lessen the fan run time when the store is closed. A suspended ceiling will work well with this type of system; conceals ductwork, supports diffusers and provides for a return air plenum.
EFFICIENCY Use a rate-of-return analysis to determine the SEER or COP levels that are most economical. Look at payback periods. Research for tax credits. Roof mounted packaged units are easy to install, conserve ground space, allow for shallow plenum depth and can be purchased in a variety of types (heat pumps; AC w/ furnace & fan unit; etc.).
OFFICE TOWER- CASE STUDY
Class A office tower with lease space and these HVAC considerations: 1. Good comfort control (for the “suits”) 2. Low operating cost 3. Low initial cost
HEATING & COOLING SELECTION
Large building that will need natural gas fired boilers for a hot water heating system. Hot water piping will serve numerous air handling units. Chillers will also be appropriate and will be housed in the same space as the boilers. Chill water piping will run alongside the hot water piping to the air handlers. Cooling towers will make the system more efficient. Use several boilers & chillers to provide for partial outages due to equipment failure.
ZONING AND EFFICIENCY Since the exterior cladding is glass, use zoned constant volume equipment with zones designed around the orientation of each face to control solar gain and night time heat loss. Use a single zone variable speed air handler for the core area with VAV boxes to further control air flow; conserve energy at night and on weekends with few people and lights.
CHURCH- CASE STUDY New church auditorium for 600 members w/ two morning services on Sundays. The church is located in a small southern town. The church’s needs are: 1. Low initial costs 2. Low operating costs
HEATING SELECTION Use a natural gas fired furnace to supply heat. Use a furnace with multiple burners so that rapid heating is available for services and lower heat is available to maintain minimum temperature at other times. If this is a rural area with mild winters a heat pump system esp. water source may be a viable alternative.
COOLING SELECTION A water source heat pump may be a viable cooling solution if a unit w/ a high COP is used. Since a large amount of energy is used during a short period before and during the services, peak electrical cost will be the largest expense. Ice tank equipment that can help shift or spread out the electrical energy use can work under this scenario.
ZONING AND EFFICIENCY Since the sanctuary is mainly a single large space- single zone, constant volume air handlers are appropriate. Since noise can be an issue, lower fan speed and oversized ductwork may be required. Since the sanctuary has limited use and is unoccupied most of the time, operating cost is not as critical as peak electrical demand.
HOTEL- CASE STUDY Moderate size, exclusive hotel w/ 500 guest rooms, meeting rooms and dining facilities. A center atrium core that extends to the roof. HVAC requirements are: 1. Individual control of guest rooms 2. Noise control between rooms (privacy) 3. Quick repairs to guest room equipment 4. Separate control of all meeting & dining rms. 5. Low operating cost 6. Heat for the atrium in winter
HOTEL CROSS SECTION
HEATING AND COOLING SELECTION
Several boilers w/ hot water piped to individual fan coil units for the guest rooms. Use single zone air handlers for each dining or meeting room. Use hot water radiant heat in the floor of the atrium. A glass ceiling could add solar gain. Use chillers to supply cold water piping to the fan coil units in the guest rooms and to the air handlers for public spaces. VAV air handlers and boxes may save energy cost in the public spaces where occupancy varies.
EFFICIENCY In an exclusive hotel quality equipment that runs quietly and efficiently when operated is a good investment; good from a guest point of view, maintenance cost and operating costs. Any waste heat from the atrium (solar gain & air against the ceiling) can be recycled, esp. in the winter).
HOTEL- OPTION #2 Choices: 1. Four pipe boiler/chiller installation w/cooling towers and fan coil units. 2. Loop connected water source heat pumps w/boiler and cooling towers.
HOTEL- OPTION #2 Choice #1: A four pipe system will typically have to run both boilers and chillers in order to provide both heating and cooling simultaneously. This is often required when heating is needed in guest rooms and cooling is needed in meeting rooms, restaurants or public spaces.
HOTEL- OPTION #2 Choice #2: Loop heat pumps are very efficient when both heating and cooling are required. When heating and cooling loads are balanced only the heat pumps need operate since they can transfer warm or cool water from the heat pumps that are producing the warm or cool water to the heat pumps that need the warm or cool water to operate efficiently. When heating loads are large the boilers will supply hot water and when the cooling loads are large the cooling towers will supply cool water.
LOOP CONNECTED WATER SOURCE HEAT PUMPS
HOME HEATING- HVAC OPTIONS
Option #1: Convectors w/ a boiler, pump & pipe loop. Option #2: Individual units (through wall) using heat pumps or AC units w/strip heat. Option #3: Single zone constant volume using a heat pump or split system with furnace and air cooled condensing unit; w/ductwork. Option #4: Radiant heat using piping embedded in the floor and zoned cooling using two single zone constant volume AC units w/ductwork.
OPTION#1- CONVECTORS Provide low cost heat but cooling is dependent on cool outside air from ventilation. Convectors are located in each room and connected by hot water piping (a two pipe reverse return system provides more even heat). Boilers can be purchased which use the cheapest fuel available locally. The boiler can also supply domestic hot water (a water heater will not be required).
OPTION #2- INDIVIDUAL UNITS
Through the wall units can provide comfortable heating/cooling. They can also be efficient esp. when the units are only operated in occupied rooms. If one unit goes out the others can still provide heating/cooling. Major disadvantages are aesthetics and noise although high quality units will be more attractive and quieter.
OPTION #3- SINGLE ZONE The most often chosen option in new homes. Heating can be a furnace w/ an air cooled condensing unit outside to supply refrigerant to the evaporator coils that are housed w/ the furnace and fan indoors (closet or attic). A heat pump can replace both the furnace and condensing unit. Ductwork is required that distributes the heated or cooled air. Larger homes may use two single zone systems.
OPTION #4- RADIANT HEAT+ZONED COOLING
Probably the most expensive system to install. The piping is usually embedded in concrete so this occurs mostly w/ new construction. Radiant heat is quiet and comfortable and operating cost is about the same as for convectors. Cooling is by two constant volume AC units; one serving the bedrooms and the other the remainder of the home. The example in you text calls for oversize supply ducts and insulated return air ducts. While this does provide for a quieter system, it also does increase initial cost. Operating cost may be slightly lower.
RADIANT HEAT+ZONED COOLING
OFFICE- HVAC OPTIONS AC/heating equipment options include heat pumps, furnaces w/DX cooling, or boilers & chillers. The options that will be considered are for zoning, not heating/cooling equipment. Option #1: Zoned w/ many heat pumps. Option #2: Zoned w/ four air handlers. Option #3: Multizoned w/one air handler. Option #4: Zoned w/ four VAV units.
OFFICE- OPTION #1 Several single zone units w/ individual air handlers are installed above the suspended ceiling. Heat pumps are used for heating & cooling. This allows individual control for each tenant and individual billing. Maintenance & service for the units is more difficult. A boiler & chiller could supply the air handlers in each space. This may give excess capacity at night & weekends and if there was a failure the entire building would be impacted. Another option would be roof mounted packaged units w/ AC & furnaces. This would require space for chases to serve the first floor.
OFFICE- OPTION #1 BUILDING CROSS SECTION EQUIPMENT LAYOUT
OFFICE- OPTION #2 This option divides the building into four zones, two on each floor. Different heating and cooling loads that result from windows (solar) on the north and south sides of the building can be addressed. Each zone is served by a single constant volume air handler. Equipment will be easy to access but will also have excess capacity at night & weekends. Equipment can be heat pumps, furnaces w/ DX cooling, or boilers and chillers.
ZONED W/ FOUR AIR HANDLERS
OFFICE- OPTION #2 ZONED W/ FOUR AIR HANDLERS (two on each floor)
OFFICE- OPTION #3 A single air handler can deliver a constant volume of warm or cool air to the entire building. This would require an individual duct bypass unit w/ heating and cooling coils for each zone (primary duct run). This would give good temperature control in each zone. More space would be required and if the air handler failed the system would fail. Initial cost would also be high.
MULTIZONE W/INDIVIDUAL DUCTS
OFFICE- OPTION #3 MULTIZONE W/INDIVIDUAL DUCTS
OFFICE- OPTION #4 There would be the same four zones as there were w/ Option #2. Four separate VAV air handlers would heat or cool each zone. There would also be VAV terminals at the end of each primary duct run to control each office or smaller area.
OFFICE- OPTION #4 ZONED W/ FOUR VAV UNITS
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