1 | weatherization assistance program standardized curriculum – december 2012eere.energy.gov hvac...
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1 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
HVAC Distribution Systems
WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY
2 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Learning Objectives
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.
HVAC DISTRIBUTION SYSTEMS
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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
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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
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Ducted Distribution System
HVAC DISTRIBUTION SYSTEMS
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Ducted Distribution System, Cont’d
HVAC DISTRIBUTION SYSTEMS
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Open Returns
Photo Courtesy of PA Weatherization Training Center
Open return
Draft hood(open at bottom)
HVAC DISTRIBUTION SYSTEMS
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Atmospheric Gas Furnace
Distribution System Components
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.
HVAC DISTRIBUTION SYSTEMS
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Function of Heat Exchanger
• 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.
HVAC DISTRIBUTION SYSTEMS
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Heat Exchanger Leakage Testing
Test methods:
1. Visual inspection
2. Inspection with small torch
3. CO reading
4. Wavering flame
5. Tracer gas
Photo courtesy of New River Center for Energy Research and Training (NRCERT)
Damaged area of heat exchanger
HVAC DISTRIBUTION SYSTEMS
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Ductwork Efficiency
• 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.
It is often necessary to remove duct insulation to properly seal ducts. Seal with mastic, then re-insulate.
Photos courtesy of NRCERT
HVAC DISTRIBUTION SYSTEMS
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Ductwork
This sheet metal ductworkis located within the building envelope, so it does not need to be insulated.Photos courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Ducted System Controls
The primary controls are:
• Thermostat.
• Fan and limit control.
• Balancing dampers.
• Motorized dampers (these are not common).
HVAC DISTRIBUTION SYSTEMS
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Furnace Thermostat
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
HVAC DISTRIBUTION SYSTEMS
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Fan and Limit Control
This control turns the air handler blower on andoff 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 isthe limit control.
Recent versions areelectronic and cannot beadjusted in the field.
Graphic source: Heating with Gas, Natural Resources Canada, 1998.Photo courtesy of Honeywell.
HVAC DISTRIBUTION SYSTEMS
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Balancing damperBalancing damper
Balancing Dampers
Graphic source: Heating with Gas, Natural Resources Canada, 1998.
Dampers help control airflow to rooms.
Manual balancing dampers are not as commonas they should be. Sometimes they need to be added.
HVAC DISTRIBUTION SYSTEMS
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Motorized Dampers
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.
Motorized dampers are uncommon.
Motorized dampers are uncommon.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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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
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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
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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).
Photo courtesy of NRCERT
Pressure pan testing of the duct
system
Pressure pan testing of the duct
system
HVAC DISTRIBUTION SYSTEMS
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• 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
Photo courtesy of NRCERT
The handle allows for easy testing of
hard-to-reach ducts.
The handle allows for easy testing of
hard-to-reach ducts.
HVAC DISTRIBUTION SYSTEMS
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Pressure Pan Use
Sample mobile home duct pattern
Bedroom0.8 Pa
Bedroom1.2 Pa
Bath2.4 Pa
Furnace Closet (living room) 2.6 PaLiving Room
2.6 PaKitchen
1.2 PaKitchen
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
HVAC DISTRIBUTION SYSTEMS
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Duct Blower for Duct Leakage
Use duct pressurization testing to quantify:
• Total duct leakage (to indoors and outdoors).
• Duct leakage to outdoors.
Photo courtesy of The Energy Conservatory
ManometerManometer
Duct blasterDuct blaster
HVAC DISTRIBUTION SYSTEMS
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Duct Blower Procedure Summary #1
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.
HVAC DISTRIBUTION SYSTEMS
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Duct Blower Procedure Summary #2
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.
HVAC DISTRIBUTION SYSTEMS
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Room-to-Room Imbalances #1
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
HVAC DISTRIBUTION SYSTEMS
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Room-to-Room Imbalances #2
MasterBedroom
Bedroom Bath
Utility Room Kitchen
Living Room
Whole-house return in hallway
HVAC DISTRIBUTION SYSTEMS
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Room-to-Room Imbalances #3
Measure room-to-room pressure imbalancesRoom pressure imbalances over 3 Pa should be remedied by adding supply or return air. Then retest.
Photo courtesy of PA Weatherization Training Center
HVAC DISTRIBUTION SYSTEMS
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Room-to-Room Imbalances #4
Graphic source: Air Distribution System Design, DOE, 2003.
Solutions1. Undercut door.
2. Add jumper duct.
3. Add door grille.
4. Add wall grille.
5. Add transfer grille.
6. Install return in affected room.
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.
HVAC DISTRIBUTION SYSTEMS
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Point the tip into the air stream
Measuring Static Pressure #1
Static pressure tip
Photo courtesy of Rob deKieffer
MagnetMagnet
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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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.
Measuring Static Pressure #2
HVAC DISTRIBUTION SYSTEMS
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External Static PressureIWC (Pa)
Air Handler Fan FlowCubic Feet per Minute
0.69 (173) 1,350
0.62 (155) 1,400
0.55 (138) 1,450
0.47 (118) 1,500
0.39 (98) 1,550
0.31 (78) 1,600
If the static pressure is too high, the fan flow will drop.
General External Static Pressure and Fan Relationship
Measuring Static Pressure #3
HVAC DISTRIBUTION SYSTEMS
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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
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• 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.
Temperature Rise Test #1
HVAC DISTRIBUTION SYSTEMS
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Measuring Temperature Rise &
Calculating CFM
Temperature Rise Test #2
The temperature rise for this example
is 70:
145 supply side
-75 return side
70 temperature rise
HVAC DISTRIBUTION SYSTEMS
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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).
Temperature Rise Test #3
HVAC DISTRIBUTION SYSTEMS
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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.
Temperature Rise Test #4
HVAC DISTRIBUTION SYSTEMS
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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
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TrueFlow® Air Handler Flow Meter
Measures airflowin residentialair handlers
#20#14
Measuring Air Flow at Air Handler #1
Photos courtesy of The Energy Conservatory
HVAC DISTRIBUTION SYSTEMS
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Airflow in CFM Furnace BTUH Input
500 Less than 60,000
700 60,000 to 79,999
900 80,000 to 99,999
1,200 More than 100,000
Measuring Air Flow at Air Handler #2
General Minimum Airflow Values
HVAC DISTRIBUTION SYSTEMS
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Analysis of Existing Ductwork - 1Interview occupants about the thermal comfort of the existing system.
Ask about:• Uncomfortable rooms.
• Excessive noise.
• Frequent cycling of furnace.
Assessing Ductwork #1
Plumbing through return duct!Plumbing through return duct!Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Analysis of Existing Ductwork - 2Inspect 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
Disconnected duct!Disconnected duct!
Photo courtesy of R. Karg
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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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
• Static pressure
• Temperature rise
• Blower CFM
Assessing Ductwork #3
Very dirty blower vanes!Very dirty blower vanes!
Photo courtesy of NRCERT
HVAC DISTRIBUTION SYSTEMS
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Analysis of Existing Ductwork - 5Determine 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
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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.
Hot water or steam distribution is often referred to as “hydronic.”
HVAC DISTRIBUTION SYSTEMS
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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
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Series Loop Hot Water System
Based on graphic from the International Association of Certified Home Inspectors, Inc.
A series loop hot water distribution system is probably the most common system layout because it is the least expensive.
HVAC DISTRIBUTION SYSTEMS
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Series Loop Hot Water Baseboard
Typical hot water baseboard distribution
Photos courtesy of Slant/Fin
Damper finDamper fin
HVAC DISTRIBUTION SYSTEMS
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Expansion Tanks
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
HVAC DISTRIBUTION SYSTEMS
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Hot Water Distribution Controls
Thermostat
Circulator pump(s)
Zone valves
Aquastat
HVAC DISTRIBUTION SYSTEMS
Basic controls include:
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Boiler Thermostat
The thermostat activatesthe boiler circulator orzone valve and circulator.
The aquastat controlsthe burner.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Boiler Aquastat
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.
Also assists with DHWtemperature control if the
water heater is tankless or indirect-fired.
Normally, the aquastat control is covered.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Zone Valves
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.
Zone valves take the place of circulators.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Potential Problems with Hot Water #1
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.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Potential Problems with Hot Water #2
Older tanks (above) shouldbe drained and refilled annually.
Newer expansion tanks (right)require very little maintenance.
Poor expansion tank maintenance
Photos courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Potential Problems with Hot Water #3
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.
Air bleeder ventAir bleeder vent
Expansion tankExpansion tank
Air in the distribution system
HVAC DISTRIBUTION SYSTEMS
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Good Steam Distribution Design
A good design:
• Provides conditioning to meet all room heating loads.
• Provides thermal comfort evenly in all conditioned rooms.
HVAC DISTRIBUTION SYSTEMS
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Steam Distribution System
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.
HVAC DISTRIBUTION SYSTEMS
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Steam Distribution Controls and Gauges
Basic controls include:
• Thermostat
• Pressure control (Pressuretrol)
• Sight or gauge glass
• Low-water cutoff
HVAC DISTRIBUTION SYSTEMS
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Steam Boiler Thermostat
The thermostat activates the steam boiler burner.
The Pressuretrol turns the burner off when the set pressure is reached.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Steam Boiler
Pressuretrol(pressure control)
Sight glass
Low-water cutoff
Oil burner
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Steam Distribution Controls
Sight (gauge) glass
Low-water cutoff
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.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Pressure Control for Steam
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.
HVAC DISTRIBUTION SYSTEMS
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One-Pipe Steam Distribution
Graphic based on Basic Steam Heating Systems, Hoffman Specialty, ITT Industries, 1999, p. 2, www.hoffmanspecialty.com.
One-Pipe Steam Distribution
Both steam and condensate use the same pipe.
Steam travels to each radiator, condenses (giving off heat), and flows back to the boiler through the same pipe as condensed water.
HVAC DISTRIBUTION SYSTEMS
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Two-Pipe Steam Distribution
Steam moves to theradiators in one pipe and the condensate flows back to the boiler through the other pipe.
These pipes are usually a smaller diameter thanone-pipe systems.
Graphic based on Basic Steam Heating Systems, Hoffman Specialty, ITT Industries, 1999, p. 2, www.hoffmanspecialty.com.
HVAC DISTRIBUTION SYSTEMS
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Potential Problems with Steam #1
Steam distribution pipesare sometimes coveredwith asbestos insulation.
If this material is friable,be careful; it might bebest to avoid blower doortesting.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
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Potential Problems with Steam #2
Air valveAir valveSupply valveSupply valve
If one- or two-piperadiators don’t heat up, the supply valve may be closed or the airvalve may be blocked.
Two-pipe radiator
Photo source: The Open Fire Centre Ltd., Yorkshire St., Oldham, Lancashire, UK. www.fireplaces-oldham.co.uk.
HVAC DISTRIBUTION SYSTEMS
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Potential Problems with Steam #3
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.
High pressure can cause distribution problems and waste energy.
Photo courtesy of Bill Van der Meer
HVAC DISTRIBUTION SYSTEMS
69 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Potential Problems with Steam #4
When replacing a steamboiler, the new unit mustbe sized to match the installed radiation, rather than the heat load of the house.
Photo courtesy of R. Karg
HVAC DISTRIBUTION SYSTEMS
70 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Summary #1
• 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.
HVAC DISTRIBUTION SYSTEMS
71 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov
Summary #2
• 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.
HVAC DISTRIBUTION SYSTEMS