Transcript HVAC Distribution Systems - Weatherization Assistance Program
WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY
HVAC Distribution Systems
1 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
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.
2 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Good Ducted System Design
HVAC DISTRIBUTION SYSTEMS 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.
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Forced Air Distribution System
HVAC DISTRIBUTION SYSTEMS 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.
4 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Ducted Distribution System
HVAC DISTRIBUTION SYSTEMS 5 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Ducted Distribution System, Cont’d HVAC DISTRIBUTION SYSTEMS 6 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Open Returns
HVAC DISTRIBUTION SYSTEMS Open return Draft hood (open at bottom)
Photo Courtesy of PA Weatherization Training Center
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Distribution System Components
HVAC DISTRIBUTION SYSTEMS Source:
Heating with Gas
, Natural Resources Canada, 1998.
8 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 Atmospheric Gas Furnace
Find the:
1. Circulating fan 2. Air filter 3. Cold air return 4. Heat exchanger 5. Warm air to house eere.energy.gov
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.
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Heat Exchanger Leakage Testing
HVAC DISTRIBUTION SYSTEMS Test methods: 1.
2.
3.
4.
5.
Visual inspection Inspection with small torch CO reading Wavering flame Tracer gas Damaged area of heat exchanger 10 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
Photo courtesy of New River Center for Energy Research and Training (NRCERT)
eere.energy.gov
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.
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Photos courtesy of NRCERT
eere.energy.gov
Ductwork
HVAC DISTRIBUTION SYSTEMS
Photos courtesy of R. Karg
This sheet metal ductwork is located within the building envelope, so it does not need to be insulated.
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Ducted System Controls
HVAC DISTRIBUTION SYSTEMS The primary controls are: • Thermostat.
• Fan and limit control.
• Balancing dampers. • Motorized dampers
(these are not common).
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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
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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.
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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.
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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
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Common Ductwork Problems
HVAC DISTRIBUTION SYSTEMS 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.
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Diagnostics for Ductwork
HVAC DISTRIBUTION SYSTEMS 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.
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Pressure Pan
HVAC DISTRIBUTION SYSTEMS
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).
Photo courtesy of NRCERT
20 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 Pressure pan testing of the duct system eere.energy.gov
Pressure Pan Procedure Summary
HVAC DISTRIBUTION SYSTEMS • Depressurize house to 50 Pa with blower door.
Photo courtesy of NRCERT
• 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.
The handle allows for easy testing of hard-to-reach ducts.
•
Goal = readings lower than 1 Pa
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Pressure Pan Use
HVAC DISTRIBUTION SYSTEMS Sample mobile home duct pattern Bedroom Bedroom Bath Furnace Closet (living room) Living Room Kitchen Kitchen 0.8 Pa 1.2 Pa 2.4 Pa 2.6 Pa 2.6 Pa 1.2 Pa 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
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Duct Blower for Duct Leakage
HVAC DISTRIBUTION SYSTEMS Use duct pressurization testing to quantify: • Total duct leakage (to indoors and outdoors).
• Duct leakage to outdoors.
Manometer Duct blaster 23 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
Photo courtesy of The Energy Conservatory
eere.energy.gov
Duct Blower Procedure Summary #1
HVAC DISTRIBUTION SYSTEMS
To test for total duct leakage:
1. Open a window or door to the outdoors.
2. Install duct blower to the air handler compartment.
3. Temporarily seal all supply registers and return grilles.
4. Insert manometer hose into a supply duct.
5. Open up rooms containing ducts.
6. Pressurize the ducts to 25 Pa and record the airflow.
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Duct Blower Procedure Summary #2
HVAC DISTRIBUTION SYSTEMS To test for duct leakage to outdoors: 1. Close all exterior windows and doors.
2. Set up blower door to pressurize the house.
3. Connect duct blower to air handler compartment and manometer hose to air handler compartment.
4. Temporarily seal all supply registers and return grilles.
5. Pressurize the ducts to 25 Pa.
6. Pressurize the house until the pressure difference of the house and the ductwork is 0 Pa.
7. Record the airflow at the duct blower.
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Room-to-Room Imbalances #1
HVAC DISTRIBUTION SYSTEMS Closed doors that prevent supply air from getting back to a return cause
positive
pressures in those rooms with supply vents. . .
…which starves the return for air, causing
negative
pressure in the zone where the return is located.
Return Supply Closed door 26 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Room-to-Room Imbalances #2
HVAC DISTRIBUTION SYSTEMS Master Bedroom Utility Room Whole-house return in hallway Kitchen Living Room Bedroom Bath 27 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Room-to-Room Imbalances #3
HVAC DISTRIBUTION SYSTEMS
Measure room-to-room pressure imbalances
Room pressure imbalances over 3 Pa should be remedied by adding supply or return air. Then retest.
Photo courtesy of PA Weatherization Training Center
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Room-to-Room Imbalances #4
HVAC DISTRIBUTION SYSTEMS Solutions 1.
2.
3.
4.
5.
6.
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 in 2 of door opening. This is the in 2 of free opening for your solution. 29 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Measuring Static Pressure #1
HVAC DISTRIBUTION SYSTEMS Magnet
Photo courtesy of Rob deKieffer
Point the tip into the air stream 30 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
Photo courtesy of R. Karg
Static pressure tip eere.energy.gov
Measuring Static Pressure #2
HVAC DISTRIBUTION SYSTEMS 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.
o Measure at inlet and outlet of blower.
o Have a clean filter in place (suggested).
o Don’t measure beyond the A/C coil unless it shipped with unit.
• Add return and supply pressures together, IGNORING the negative sign.
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Measuring Static Pressure #3
HVAC DISTRIBUTION SYSTEMS General External Static Pressure and Fan Relationship External Static Pressure IWC (Pa) 0.69 (173) 0.62 (155) 0.55 (138) 0.47 (118) 0.39 (98) 0.31 (78) Air Handler Fan Flow Cubic Feet per Minute 1,350 1,400 1,450 1,500 1,550 1,600 If the static pressure is too high, the fan flow will drop.
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Measuring Static Pressure #4
HVAC DISTRIBUTION SYSTEMS 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.
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Temperature Rise Test #1
HVAC DISTRIBUTION SYSTEMS • Place thermometer in supply side as close to furnace as possible but out of “sight” of the heat exchanger. o Use manufacturer’s recommended measurement method, or o 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.
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Temperature Rise Test #2
HVAC DISTRIBUTION SYSTEMS Measuring Temperature Rise & Calculating CFM 35 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 The temperature rise for this example is 70 :
145
supply side -
75
return side
70
temperature rise eere.energy.gov
Temperature Rise Test #3
HVAC DISTRIBUTION SYSTEMS Excessive temperature rise can result from: • Low fan output.
o 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.
o Undersized or restricted ducts, dirty filter, dirty cooling coil.
• Overfired burner (gas pressure or oil nozzle).
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Temperature Rise Test #4
HVAC DISTRIBUTION SYSTEMS Low temperature rise can result from: • Excessive fan speed.
• Excessive duct leakage.
• Underfired burner.
o Low gas pressure.
o Oil nozzle not matched with airflow rate.
37 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Temperature Rise Test #5
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.
38 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Measuring Air Flow at Air Handler #1
HVAC DISTRIBUTION SYSTEMS TrueFlow ® Air Handler Flow Meter Measures airflow in residential air handlers
#20 #14
Photos courtesy of The Energy Conservatory
39 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Measuring Air Flow at Air Handler #2
HVAC DISTRIBUTION SYSTEMS General Minimum Airflow Values Airflow in CFM 500 700 900 1,200 Furnace BTUH Input Less than 60,000 60,000 to 79,999 80,000 to 99,999 More than 100,000 40 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Assessing Ductwork #1
HVAC DISTRIBUTION SYSTEMS existing system.
Ask about: • Uncomfortable rooms.
• Excessive noise.
• Frequent cycling of furnace.
Plumbing through return duct!
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Photo courtesy of R. Karg
eere.energy.gov
Assessing Ductwork #2
HVAC DISTRIBUTION SYSTEMS
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.
Photo courtesy of R. Karg
Disconnected duct!
Photo courtesy of R. Karg
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Assessing Ductwork #3
HVAC DISTRIBUTION SYSTEMS Do technical testing and appraisal of the duct system and equipment.
• Duct leakage o Pressure pan testing o Duct blower testing • Room-to-room pressure imbalances Very dirty blower vanes!
• Static pressure • Temperature rise • Blower CFM
Photo courtesy of NRCERT
43 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Assessing Ductwork #4
HVAC DISTRIBUTION SYSTEMS
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.
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Good Hot Water Distribution Design
HVAC DISTRIBUTION SYSTEMS Good design: • Provides conditioning to meet all room heating loads.
• Provides thermal comfort evenly in all conditioned rooms.
• Heats the dwelling quietly.
Hot water or steam distribution is often referred to as “hydronic.” 45 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Hot Water Distribution System
HVAC DISTRIBUTION SYSTEMS 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.
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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.
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Series Loop Hot Water Baseboard
HVAC DISTRIBUTION SYSTEMS Typical hot water baseboard distribution Damper fin 48 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
Photos courtesy of Slant/Fin
eere.energy.gov
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.
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Photos courtesy of R. Karg
eere.energy.gov
Hot Water Distribution Controls
HVAC DISTRIBUTION SYSTEMS Basic controls include: Thermostat Circulator pump(s) Zone valves Aquastat 50 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Boiler Thermostat
HVAC DISTRIBUTION SYSTEMS The thermostat activates the boiler circulator or zone valve and circulator.
The aquastat controls the burner.
Photo courtesy of R. Karg
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Boiler Aquastat
HVAC DISTRIBUTION SYSTEMS An aquastat: 1. Maintains boiler water temperature.
2. Provides high-limit temperature protection.
3. Will not allow circulator to operate if boiler water temperature is too low.
Photo courtesy of R. Karg Normally, the aquastat control is covered.
Also assists with DHW temperature control if the water heater is tankless or indirect-fired.
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Zone Valves
HVAC DISTRIBUTION SYSTEMS
Photo courtesy of R. Karg Zone valves take the place of circulators.
53 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 Zone valves are controlled by thermostats in each zone.
This house has 3 zones with one thermostat for each.
The 4th zone valve is for domestic hot water from the boiler.
eere.energy.gov
Potential Problems with Hot Water #1
HVAC DISTRIBUTION SYSTEMS
Photo courtesy of R. Karg
Poor maintenance: • If a hot water distribution system is maintained properly, there is little that can go wrong.
o Oil-fired boilers should be cleaned and tuned every year.
o Gas-fired boilers should be cleaned and tuned once every three years.
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Potential Problems with Hot Water #2
HVAC DISTRIBUTION SYSTEMS Poor expansion tank maintenance Older tanks (above) should be drained and refilled annually.
Newer expansion tanks (right) require very little maintenance.
Photos courtesy of R. Karg
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Potential Problems with Hot Water #3
HVAC DISTRIBUTION SYSTEMS Air bleeder vent Air in the distribution system If the air bleeder valve malfunctions, air will not be purged from the distribution system.
This air (oxygen) will create sludge and make the system noisy as the air is pumped with the water.
Expansion tank 56 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Good Steam Distribution Design
HVAC DISTRIBUTION SYSTEMS A good design: • Provides conditioning to meet all room heating loads.
• Provides thermal comfort evenly in all conditioned rooms.
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Steam Distribution System
HVAC DISTRIBUTION SYSTEMS The parts include: • A thermostat(s) that activates the circulator pump.
• Pressure control (Pressuretrol).
• A heat exchanger where the heat from combustion is transferred to the distribution water/vapor.
• Supply and return piping at boiler.
o For one-pipe distribution, the supply and return pipes are the same.
o For two-pipe distribution, there are separate supply and return pipes.
• Steam radiators that transfer thermal energy to the conditioned rooms.
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Steam Distribution Controls and Gauges HVAC DISTRIBUTION SYSTEMS Basic controls include: • Thermostat • Pressure control (Pressuretrol) • Sight or gauge glass • Low-water cutoff 59 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Steam Boiler Thermostat
HVAC DISTRIBUTION SYSTEMS The thermostat activates the steam boiler burner.
The Pressuretrol turns the burner off when the set pressure is reached.
Photo courtesy of R. Karg
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Steam Boiler
HVAC DISTRIBUTION SYSTEMS Pressuretrol (pressure control) Sight glass Low-water cutoff
Photo courtesy of R. Karg
61 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 Oil burner eere.energy.gov
Steam Distribution Controls
HVAC DISTRIBUTION SYSTEMS
Photo courtesy of R. Karg
Sight (gauge) glass The low-water cutoff will shut off the burner if the water falls to an unsafe level. This is required by code.
The sight or gauge glass provides an easy way to determine the water level in a steam boiler.
Low-water cutoff 62 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Pressure Control for Steam
HVAC DISTRIBUTION SYSTEMS
Photo courtesy of Honeywell Controls
This device determines the operating range of the boiler during the heating cycle.
When the thermostat calls for heat, the burner will cycle up to the cut out pressure setting of the Pressuretrol. The burner will then shut off.
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One-Pipe Steam Distribution
HVAC DISTRIBUTION SYSTEMS
One-Pipe Steam Distribution
Both steam and condensate use the same pipe.
Graphic based on Basic Steam Heating Systems, Hoffman Specialty, ITT Industries, 1999, p. 2, www.hoffmanspecialty.com
.
64 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 Steam travels to each radiator, condenses (giving off heat), and flows back to the boiler through the same pipe as condensed water.
eere.energy.gov
Two-Pipe Steam Distribution
HVAC DISTRIBUTION SYSTEMS
Graphic based on Basic Steam Heating Systems, Hoffman Specialty, ITT Industries, 1999, p. 2, www.hoffmanspecialty.com
.
65 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 Steam moves to the radiators in one pipe and the condensate flows back to the boiler through the other pipe.
These pipes are usually a smaller diameter than one-pipe systems.
eere.energy.gov
Potential Problems with Steam #1
HVAC DISTRIBUTION SYSTEMS Steam distribution pipes are sometimes covered with asbestos insulation.
If this material is friable, be careful; it might be best to avoid blower door testing.
Photo courtesy of R. Karg
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Potential Problems with Steam #2
HVAC DISTRIBUTION SYSTEMS Supply valve Air valve If one- or two-pipe radiators don’t heat up, the supply valve may be closed or the air valve may be blocked.
Two-pipe radiator
Photo source: The Open Fire Centre Ltd., Yorkshire St., Oldham, Lancashire, UK. www.fireplaces-oldham.co.uk
.
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Potential Problems with Steam #3
HVAC DISTRIBUTION SYSTEMS Steam pressure is often set too high. This can cause distribution problems and wastes energy.
For most residential low-pressure, one pipe systems, 2 psi cut-out pressure or less will work fine and maximize efficiency.
Photo courtesy of Bill Van der Meer
High pressure can cause distribution problems and waste energy.
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Potential Problems with Steam #4
HVAC DISTRIBUTION SYSTEMS When replacing a steam boiler, the new unit must be sized to match the installed radiation, rather than the heat load of the house.
Photo courtesy of R. Karg
69 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Summary #1
HVAC DISTRIBUTION SYSTEMS • The function of all distribution systems is to provide even thermal comfort in all rooms of the home. • Major components of forced air distribution systems include an air handler, heat exchanger, supply air plenum, supply and return registers, grilles, branches, and ducts.
• Forced air system diagnostic procedures include duct leakage testing, measuring static pressure, temperature rise, room-to room pressure imbalances, and airflow across the heat exchanger.
• Common problems associated with ducted systems include room pressure imbalances, improper temperature rise, and energy wasted through duct leakage to the outdoors. 70 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Summary #2
HVAC DISTRIBUTION SYSTEMS • Major components of hot water distribution systems include the thermostat, circulator pump, aquastat control, heat exchanger, supply and return piping, expansion tank, and hot water baseboard units.
• Major components of steam distribution systems include the thermostat, pressure control (Pressuretrol), heat exchanger, supply and return piping at the boiler, steam radiators, sight glass or gauge glass, and low-water cutoff.
• Some common problems associated with hot water or steam distribution include expansion tank degradation, low water levels (steam), or improper sizing once the home is weatherized.
• Compared with ductwork, hot water and steam distribution are relatively trouble-free, and diagnostic procedures are easy. We merely ask the occupants if there are problems with the thermal comfort of the home and conduct a simple inspection of the distribution components.
71 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov