Chapter 21Heating, Ventilating, and Air-

Conditioning (HVAC)

Overview

HVAC Drawings

Code RequirementsHeating Systems

Zone Control

3 Methods of Heat Transfer?Hint (C.C.R)

Introduction• Heating, ventilating, and air-conditioning

(HVAC)– Heating and air-conditioning equipment, and

systems found in a building• Also referred to as the mechanical system• Regulates temperature

– International Residential Code (IRC) • Requires a heating unit in any residence built in an

area where winter design temperature is below 60°

Thermal Calculations for Heating/Cooling

• Necessary to establish the correct:– Furnace– Ductwork– Supply– Return register specifications

• Historical primary use – Calculate design heat load of houses to estimate

gas and oil heating systems size

Thermal Calculations for Heating/Cooling (cont’d.)

• HVAC terminology:– Btu– Indoor Air Quality (IAQ)– Duct loss– Cubic Feet/ Min. (CFM)– Heat transfer multiplier– Indoor temperature– Air Changes per Hour (ACH)

– Indoor wet bulb– Infiltration– Internal heat gain– Latent load– Mechanical

ventilation

Thermal Calculations for Heating/Cooling (cont’d.)

• HVAC terminology (cont’d.):– Outdoor temperature– Outdoor wet bulb– R-factor– Sensible load calculations– Temperature difference– U-factor

Thermostats• Automatic mechanism for controlling

heating or cooling by a central or zonal system– Location is important

Exhaust Systems: Code Requirements

• Exhausts are part of the HVAC system– Exhaust systems are required to remove

odors, steam, moisture, and pollutants • Refer to the text for basic general code

requirements

HVAC Code Requirements• National Energy Conservation Code

regulates the design and construction of:– Exterior envelope and selection of HVAC– Service water heating– Electrical distribution – Illuminating systems and required equipment

• Refer to the text for general code requirements

Code Requirements IECC is updated every three years and is designed to

provide an energy efficient environment for humans Equipment in a garage must be protected from

automobile impact (slab on grade construction would have a 18” platform)

Programmable Thermostat Exterior (Building) envelope is space that is heated

and cooled• Conditioned (finished square footage)• Unconditioned (basement unfinished)

- Must be separated by a door

Code Requirements A door or access large enough to remove largest piece of equipment Unobstructed working space not less than 30” wide and high should

be provided next to the control side of the equipment (Furnace, WH) An GFCI electrical outlet and lighting fixture should be provided near

the equipment and have a switch at the doorway or access (In attic) Equipment located on the ground should be supported on a concrete

slab and be at least 3” above the ground. (AC units) Fuel burning warm-air furnaces must be supplied with combustion air All exterior ducting (Avoid at all costs) should be weatherproof and

insulated In basements all supply lines should be insulated with R-4.2

insulation unless wall drapes are used to consider it conditioned space

Minimum Dimensions•Furnace 24 x 30•Water Heater 18-24” Diameter•Electrical Panel 30” open space•Pex Piping

Duct Systems

•Cold Air Return•Supply

Central Forced-Air Systems

Forced Air Systems A fan forces air into

ducts that connect to air supply registers

Air is heated during the heating cycle and the combustion is vented out flue

Cooled air is passed over a cooling coil which is cooled with a refrigerant (Puron)

Forced-Air Heating Plans• Complete forced-air heating plans show:

– Size, location, and number of British thermal units (Btu) dispersed from warm-air supplies

– Location and size of cold-air return – Location, type, and output of furnace

• Providing duct space (i.e., chase)– When ducted heating and cooling systems are

used, duct location becomes important

Central Air Systems

Rules to Design1.Place Central Air Condenser unit at shortest straight line to exterior side or rear of home for coil (efficiency)

2. Place Ducting trunks cold air returns and supply lines to one side of bearing wall (Stairs)

3. Add Combustion Air Intake direct line same direction floor joist are running

Zone Control Systems• One heater and one thermostat per room

– No duct work– Only heaters in occupied rooms need to be

turned on• Types:

– Baseboard– Fan heaters– Split systems

Alternate Method using Zone Controls Individual rooms are heated and

cooled as needed

Hot Water System Water is circulated through a radiator after

being heated in an oil- or gas-fired boiler One-pipe system has heated water pass

through radiators and returns in the same pipe to the boiler

Radiant Flooring is growing in popularity

Hot Water Systems• Water is heated in an oil- or gas-fired boiler

– Then circulated through pipes to radiators or convectors

Radiant Heat• Radiant heating and cooling systems

– Control surface temperatures – Minimize excessive air motion– Annual operating cost savings of 20% to 50%

• Lower thermostat settings • Superior, cost-effective design

Heat Pump/ Geothermal / Passive Solar Systems Heat is extracted from outside air and pumped

through a compressor into the structure Heat pump systems are 30 to 50 percent more

efficient then forced air systems Air is cleaner and fresher with a heat pump system

Heat Pump Systems• Forced-air central heating and cooling

system – Compressor and circulating refrigerant system

Exhaust System Code Requirements

Vented hoods must have back draft damper• Direct vent to exterior suggested for gas or

exhaust fan in kitchen If gas dryer or other fuel burning appliance (Fan is

good idea) Clothes dryer vents independent from all other

systems.• No screws in vent• Back draft damper• 4” duct no longer than 25’

- Total length reduced 2.5’ for each 45 bend and 5’ for each 90 bend

Heat Recovery and Ventilation • Uses a counter flow heat exchanger

between inbound and outbound airflow– Air pollutants

• Principle reason for installation– Air-to-air heat exchangers

• Pulls polluted, stale, warm air from the space and transfers heat in that air to fresh, cold air being pulled into the space

Gas lines

Meter Pressurized Gas

• 2lb• 4 oz

HVAC Drawings• Drawings for the HVAC system show:

– Size and location of all equipment, ductwork, and components

– Use accurate symbols, specifications, notes, and schedules

• Form the basis of contract requirements for construction

Residential HVAC DrawingsShow Thermostat locationHeat Register Locations

4 x 10 floor or 2 x 10 under cabinet

Cold air return is needed for every 5 heat registers

14 x 8 single or 30 x 8 double

Size of room and use determines number of registers needed ~ 150 square feet = Single

Residential HVAC DrawingsShow Supply and Return Main Trunk LinesDryer Vent Location Combustion Air Location