HVAC Distribution Systems • WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY
Learning Objectives HVAC DISTRIBUTION SYSTEMS • By attending this session, participants will be able to: • Name functions of the components of forced warm air, hot water, and steam distribution systems. • Demonstrate common diagnostic and assessment methods for ducted distribution systems. • Describe common problems for each distribution system type. • Explain solutions to these common problems.
Good Ducted System Design A well-designed duct system: Provides conditioned air to meet all room heating loads. Provides thermal comfort evenly in all conditioned rooms. Is properly sized so that static pressure is within manufacturer specifications. Is sealed to provide proper airflow and prevent air from entering the house or duct system from polluted zones. Has balanced supply and return airflows to maintain a neutral pressure in the house. Minimizes duct air temperature losses between the air handler and supply registers. HVAC DISTRIBUTION SYSTEMS
Forced Air Distribution System The parts include: An air handler at the furnace. A heat exchanger where the heat from combustion is transferred to the distribution air. A supply air plenum to which the supply trunks are attached. Branches attached to the supply trunk. Supply registers through which conditioned air flows to the living space. Return grilles through which air flows back to the furnace. Return branches and trunks attached to the return plenum. HVAC DISTRIBUTION SYSTEMS
Ducted Distribution System HVAC DISTRIBUTION SYSTEMS
Ducted Distribution System, Cont’d HVAC DISTRIBUTION SYSTEMS
Open Returns HVAC DISTRIBUTION SYSTEMS Open return Draft hood(open at bottom) Photo Courtesy of PA Weatherization Training Center
Atmospheric Gas Furnace Distribution System Components HVAC DISTRIBUTION SYSTEMS Find the: 1. Circulating fan 2. Air filter 3. Cold air return 4. Heat exchanger 5. Warm air to house Source: Heating with Gas, Natural Resources Canada, 1998.
Function of Heat Exchanger HVAC DISTRIBUTION SYSTEMS • The furnace heat exchanger is where the heat from combustion gases—usually between 70% and 95%— is transferred to the distribution air in the ductwork. • The heat exchanger is an extremely important part of any furnace because it can have a significant impact on efficiency and health and safety. • Combustion byproducts must not mix with distribution air.
Heat Exchanger Leakage Testing Test methods: Visual inspection Inspection with small torch CO reading Wavering flame Tracer gas HVAC DISTRIBUTION SYSTEMS Damaged area of heat exchanger Photo courtesy of New River Center for Energy Research and Training (NRCERT)
Ductwork Efficiency HVAC DISTRIBUTION SYSTEMS • Specify duct sealing where ducts are located in unconditioned spaces. • Ducts in unconditioned spaces should be insulated to recommended levels. • Seal all returns in spaces where atmospheric fossil fuel appliances are located. It is often necessary to remove duct insulation to properly seal ducts. Seal with mastic, then re-insulate. Photos courtesy of NRCERT
Ductwork HVAC DISTRIBUTION SYSTEMS This sheet metal ductwork is located within the building envelope, so it does not need to be insulated. Photos courtesy of R. Karg
Ducted System Controls The primary controls are: Thermostat. Fan and limit control. Balancing dampers. Motorized dampers (these are not common). HVAC DISTRIBUTION SYSTEMS
Furnace Thermostat HVAC DISTRIBUTION SYSTEMS The thermostat activates the burner on a furnace. The fan and limit switch turns the air handler blower on and off. Photo courtesy of R. Karg
Fan and Limit Control HVAC DISTRIBUTION SYSTEMS This control turns the air handler blower on and off at set temperatures. This is the fan control. It also shuts down the blower if the heat exchanger area gets too hot (usually at about 200). This is the limit control. Recent versions are electronic and cannot be adjusted in the field. Graphic source: Heating with Gas, Natural Resources Canada, 1998. Photo courtesy of Honeywell.
Balancing Dampers HVAC DISTRIBUTION SYSTEMS Dampers help control airflow to rooms. Balancing damper Graphic source: Heating with Gas, Natural Resources Canada, 1998. Manual balancing dampers are not as common as they should be. Sometimes they need to be added.
Motorized Dampers HVAC DISTRIBUTION SYSTEMS Motorized dampers are uncommon. Motorized dampers are used for zoning a ducted distribution system, rather than for balancing. When a zone requires heat, the thermostat of that zone opens the zone damper and activates the furnace burner. Photo courtesy of R. Karg
Common Ductwork Problems Common problems include: Duct leakage to/from the outdoors. Restricted return side. System not balanced. Temperature too high or too low at heat exchanger. Static pressure out of range. Airflow of air handler fan not matched to system. People live within the distribution system. Closing a bedroom door or covering a register or grille can significantly alter airflow. HVAC DISTRIBUTION SYSTEMS
Diagnostics for Ductwork Diagnostics include: Pressure pan (duct leakage). Duct blower (duct leakage). Static pressure. Temperature rise. Room-to-room pressure differences (door restrictions). Air handler blower CFM flow. HVAC DISTRIBUTION SYSTEMS
Pressure Pan Test the duct system with a pressure pan and blower door to identify: Leakage to the outdoors when ducts are located outside the thermal boundary. Leakage pathways from duct-containing building cavities to the outdoors (e.g., floor-joist cavities adjacent to porch roofs, cantilevers). HVAC DISTRIBUTION SYSTEMS Pressure pan testing of the duct system Photo courtesy of NRCERT
Depressurize house to 50 Pa with blower door. Test each register and grille. Document readings. Registers too large or oddly shaped may be covered with plastic and taped on edges. Seal duct leaks and retest. Goal = readings lower than 1 Pa Pressure Pan Procedure Summary HVAC DISTRIBUTION SYSTEMS Photo courtesy of NRCERT The handle allows for easy testing of hard-to-reach ducts.
Pressure Pan Use HVAC DISTRIBUTION SYSTEMS Sample mobile home duct pattern Bedroom 0.8 Pa Bedroom 1.2 Pa Bath 2.4 Pa Furnace Closet (living room) 2.6 Pa Living Room 2.6 Pa Kitchen 1.2 Pa Kitchen 0.5 Pa Total: 10.7 Pa 2.4 Pa at the bath register and 2.6 Pa at the living room register indicate a large leak between them, probably at the furnace plenum. Photo courtesy of NRCERT
Duct Blower for Duct Leakage Use duct pressurization testing to quantify: Total duct leakage (to indoors and outdoors). Duct leakage to outdoors. HVAC DISTRIBUTION SYSTEMS Manometer Duct blaster Photo courtesy of The Energy Conservatory
Duct Blower Procedure Summary #1 To test for total duct leakage: Open a window or door to the outdoors. Install duct blower to the air handler compartment. Temporarily seal all supply registers and return grilles. Insert manometer hose into a supply duct. Open up rooms containing ducts. Pressurize the ducts to 25 Pa and record the airflow. HVAC DISTRIBUTION SYSTEMS
Duct Blower Procedure Summary #2 To test for duct leakage to outdoors: Close all exterior windows and doors. Set up blower door to pressurize the house. Connect duct blower to air handler compartment and manometer hose to air handler compartment. Temporarily seal all supply registers and return grilles. Pressurize the ducts to 25 Pa. Pressurize the house until the pressure difference of the house and the ductwork is 0 Pa. Record the airflow at the duct blower. HVAC DISTRIBUTION SYSTEMS
Room-to-Room Imbalances #1 HVAC DISTRIBUTION SYSTEMS Closed doors that prevent supply air from getting back to a return cause positivepressures in those rooms with supply vents. . . …which starves the return for air, causing negativepressure in the zone where the return is located. Return Supply Closed door
Room-to-Room Imbalances #2 HVAC DISTRIBUTION SYSTEMS Master Bedroom Utility Room Kitchen Whole-house return in hallway Living Room Bedroom Bath
Room-to-Room Imbalances #3 Measure room-to-room pressure imbalances Room pressure imbalances over 3 Pa should be remedied by adding supply or return air. Then retest. HVAC DISTRIBUTION SYSTEMS Photo courtesy of PA Weatherization Training Center
Room-to-Room Imbalances #4 HVAC DISTRIBUTION SYSTEMS • Solutions • Undercut door. • Add jumper duct. • Add door grille. • Add wall grille. • Add transfer grille. • Install return in affected room. Graphic source: Air Distribution System Design, DOE, 2003. Find the size of the free vent area of your solution by opening the door while the air handler is running. When the manometer reading falls below 3 Pa, measure the in2 of door opening. This is the in2 of free opening for your solution.
Measuring Static Pressure #1 HVAC DISTRIBUTION SYSTEMS Magnet Photo courtesy of Rob deKieffer Photo courtesy of R. Karg Point the tip into the air stream Static pressure tip
Measuring External Static Pressure Check nameplate for External Static Pressure (ESP). Measure both return and supply sides of the air handler as the unit was shipped. Measure at inlet and outlet of blower. Have a clean filter in place (suggested). Don’t measure beyond the A/C coil unless it shipped with unit. Add return and supply pressures together, IGNORING the negative sign. Measuring Static Pressure #2 HVAC DISTRIBUTION SYSTEMS
Measuring Static Pressure #3 HVAC DISTRIBUTION SYSTEMS General External Static Pressure and Fan Relationship If the static pressure is too high, the fan flow will drop.
Measuring External Static Pressure If ESP is too high, the airflow might be blocked or the ductwork might be too small or restricted. If ESP is too low, the ductwork might be very leaky or the fan might be dirty or damaged. Typical ESP totals are around 0.5 IWC or 125 Pa with an air conditioning coil and filter. Typical ESP totals are around 0.25 IWC or 62 Pa without an air conditioning coil and filter. It is preferred to have the return and supply sides of similar magnitudes, for example, a return of -34 Pa and supply of +31 Pa. Measuring Static Pressure #4 HVAC DISTRIBUTION SYSTEMS
Place thermometer in supply side as close to furnace as possible but out of “sight” of the heat exchanger. Use manufacturer’s recommended measurement method, or Use the four-corner method (measure at each corner or supply plenum and average readings). Place thermometer in return side. Fire furnace. When the supply-side temperature reaches steady state, subtract return-side from supply-side temperature to get temperature rise. Check specified temperature rise on furnace name plate. Actual should be in the middle of the nameplate range. Temperature Rise Test #1 HVAC DISTRIBUTION SYSTEMS
Measuring Temperature Rise &Calculating CFM Temperature Rise Test #2 HVAC DISTRIBUTION SYSTEMS The temperature rise for this example is 70: 145supply side -75return side 70temperature rise
Excessive temperature rise can result from: Low fan output. Wrong fan speed, bad motor bearings, low voltage to motor, dirty blower wheel, wrong motor rotation, slipping blower belt. Low airflow from restrictions in system. Undersized or restricted ducts, dirty filter, dirty cooling coil. Overfired burner (gas pressure or oil nozzle). Temperature Rise Test #3 HVAC DISTRIBUTION SYSTEMS
Low temperature rise can result from: Excessive fan speed. Excessive duct leakage. Underfired burner. Low gas pressure. Oil nozzle not matched with airflow rate. Temperature Rise Test #4 HVAC DISTRIBUTION SYSTEMS
Temperature rise that is too high can: Damage the heat exchanger. Cause rocking on the high limit. Temperature rise that is too low can: Lead to condensation. Cause excessive soot buildup. Lead to occupant discomfort. Temperature Rise Test #5 HVAC DISTRIBUTION SYSTEMS
TrueFlow® Air Handler Flow Meter Measuring Air Flow at Air Handler #1 HVAC DISTRIBUTION SYSTEMS Measures airflow in residential air handlers #20 #14 Photos courtesy of The Energy Conservatory
Measuring Air Flow at Air Handler #2 HVAC DISTRIBUTION SYSTEMS General Minimum Airflow Values
Analysis of Existing Ductwork - 1 Interview occupants about the thermal comfort of the existing system. Ask about: Uncomfortable rooms. Excessive noise. Frequent cycling of furnace. Assessing Ductwork #1 HVAC DISTRIBUTION SYSTEMS Plumbing through return duct! Photo courtesy of R. Karg
Analysis of Existing Ductwork - 2 Inspect air handler and ductwork for such things as: Disconnected ducts. Duct leakage. Restricted returns. Panned floor joists. Ducts in unconditioned spaces. Balancing dampers. Assessing Ductwork #2 HVAC DISTRIBUTION SYSTEMS Disconnected duct! Photo courtesy of R. Karg Photo courtesy of R. Karg
Do technical testing and appraisal of the duct system and equipment. Duct leakage Pressure pan testing Duct blower testing Room-to-room pressure imbalances Static pressure Temperature rise Blower CFM Assessing Ductwork #3 HVAC DISTRIBUTION SYSTEMS Very dirty blower vanes! Photo courtesy of NRCERT
Analysis of Existing Ductwork - 5 Determine strategies for duct repair: Write down possible problems. Determine required alterations to furnace and ductwork. Decide on consumer education strategies. Assessing Ductwork #4 HVAC DISTRIBUTION SYSTEMS
Good Hot Water Distribution Design Good design: Provides conditioning to meet all room heating loads. Provides thermal comfort evenly in all conditioned rooms. Heats the dwelling quietly. HVAC DISTRIBUTION SYSTEMS Hot water or steam distribution is often referred to as “hydronic.”
Hot Water Distribution System The parts include: Thermostat(s) that activate the circulator pump. Circulator pump(s). Might include zone valves rather than two or more circulator pumps. Aquastat control. A heat exchanger where the heat from combustion is transferred to the distribution water. Supply and return piping at boiler. The expansion tank. Hot water baseboard units (convector) where the thermal energy is transferred to the conditioned rooms. HVAC DISTRIBUTION SYSTEMS
Series Loop Hot Water System HVAC DISTRIBUTION SYSTEMS A series loop hot water distribution system is probably the most common system layout because it is the least expensive. Based on graphic from the International Association of Certified Home Inspectors, Inc.
Series Loop Hot Water Baseboard HVAC DISTRIBUTION SYSTEMS Typical hot water baseboard distribution Damper fin Photos courtesy of Slant/Fin
Expansion Tanks HVAC DISTRIBUTION SYSTEMS Old-style tanks (above) and newer tanks (right) allow for expansion of heated water and contraction of cool distribution water. Photos courtesy of R. Karg
Hot Water Distribution Controls Thermostat Circulator pump(s) Zone valves Aquastat HVAC DISTRIBUTION SYSTEMS Basic controls include: