Chapter 21
description
Transcript of Chapter 21
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