HVAC Distribution Systems
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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.

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Hvac distribution systems

HVAC Distribution Systems

  • WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY


Learning objectives

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

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

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

Ducted Distribution System

HVAC DISTRIBUTION SYSTEMS


Ducted distribution system cont d

Ducted Distribution System, Cont’d

HVAC DISTRIBUTION SYSTEMS


Open returns

Open Returns

HVAC DISTRIBUTION SYSTEMS

Open return

Draft hood(open at bottom)

Photo Courtesy of PA Weatherization Training Center


Atmospheric gas furnace

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

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

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

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

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

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

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

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

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

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 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 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

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


Hvac distribution systems

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

Pressure Pan Use

HVAC DISTRIBUTION SYSTEMS

Sample mobile home duct pattern

Bedroom0.8 Pa

Bedroom1.2 Pa

Bath2.4 Pa

Furnace Closet (living room)2.6 Pa

Living Room2.6 Pa

Kitchen1.2 Pa

Kitchen0.5 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

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

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

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

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

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

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

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.


Hvac distribution systems

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

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


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 pressure1

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


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

Measuring Temperature Rise &Calculating CFM

Temperature Rise Test #2

HVAC DISTRIBUTION SYSTEMS

The temperature rise for this example is 70:

145supply side

-75return side

70temperature rise


Hvac distribution systems

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


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


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

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


Hvac distribution systems

Measuring Air Flow at Air Handler #2

HVAC DISTRIBUTION SYSTEMS

General Minimum Airflow Values


Analysis of existing ductwork 1

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

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


Hvac distribution systems

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

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 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

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

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

Series Loop Hot Water Baseboard

HVAC DISTRIBUTION SYSTEMS

Typical hot water baseboard distribution

Damper fin

Photos courtesy of Slant/Fin


Expansion tanks

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

Hot Water Distribution Controls

Thermostat

Circulator pump(s)

Zone valves

Aquastat

HVAC DISTRIBUTION SYSTEMS

Basic controls include:


Boiler thermostat

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


Boiler aquastat

Boiler Aquastat

HVAC DISTRIBUTION SYSTEMS

  • An aquastat:

  • Maintains boiler water temperature.

  • Provides high-limit temperature protection.

  • Will not allow circulator to operate if boiler water temperature is too low.

  • Also assists with DHW

  • temperature control if the water heater is tankless or indirect-fired.

Photo courtesy of R. Karg

Normally, the aquastat control is covered.


Zone valves

Zone Valves

HVAC DISTRIBUTION SYSTEMS

  • 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.

Photo courtesy of R. Karg

Zone valves take the place of circulators.


Potential problems with hot water 1

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.

    • Oil-fired boilers should be cleaned and tuned every year.

    • Gas-fired boilers should be cleaned and tuned once every three years.


Potential problems with hot water 2

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


Potential problems with hot water 3

Potential Problems with Hot Water #3

Air bleeder vent

Expansion tank

HVAC DISTRIBUTION SYSTEMS

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.


Good steam distribution design

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


Steam distribution system

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.

For one-pipe distribution, the supply and return pipes are the same.

For two-pipe distribution, there are separate supply and return pipes.

Steam radiators that transfer thermal energy to the conditioned rooms.

HVAC DISTRIBUTION SYSTEMS


Steam distribution controls and gauges

Steam Distribution Controls and Gauges

Basic controls include:

Thermostat

Pressure control (Pressuretrol)

Sight or gauge glass

Low-water cutoff

HVAC DISTRIBUTION SYSTEMS


Steam boiler thermostat

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


Steam boiler

Steam Boiler

HVAC DISTRIBUTION SYSTEMS

Pressuretrol

(pressure control)

Sight glass

Low-water cutoff

Oil burner

Photo courtesy of R. Karg


Steam distribution controls

Steam Distribution Controls

Sight (gauge) glass

Low-water cutoff

HVAC DISTRIBUTION SYSTEMS

Photo courtesy of R. Karg

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.


Pressure control for steam

Pressure Control for Steam

HVAC DISTRIBUTION SYSTEMS

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.

Photo courtesy of Honeywell Controls


One pipe steam distribution

One-Pipe Steam Distribution

One-Pipe Steam Distribution

HVAC DISTRIBUTION SYSTEMS

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.

Graphic based on Basic Steam Heating Systems, Hoffman Specialty, ITT Industries, 1999, p. 2, www.hoffmanspecialty.com.


Hvac distribution systems

Two-Pipe Steam Distribution

HVAC DISTRIBUTION SYSTEMS

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.

Graphic based on Basic Steam Heating Systems, Hoffman Specialty, ITT Industries, 1999, p. 2, www.hoffmanspecialty.com.


Potential problems with steam 1

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


Hvac distribution systems

Potential Problems with Steam #2

HVAC DISTRIBUTION SYSTEMS

If one- or two-pipe

radiators don’t heat up,

the supply valve may be closed or the air

valve may be blocked.

Supply valve

Air valve

Two-pipe radiator

Photo source: The Open Fire Centre Ltd., Yorkshire St.,

Oldham, Lancashire, UK. www.fireplaces-oldham.co.uk.


Hvac distribution systems

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.


Hvac distribution systems

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


Summary 1

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.


Summary 2

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.


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