2. HVAC
• Heating, Ventilation and Air
Conditioning
• Provides comfort for people
• Allows humans to exist under
adverse conditions.
3. Comfort
• Comfort is primary intent
of HVAC systems.
• Productivity
• Building Durability
• Health
• Mold
4. Load Calculations
• Heating and Cooling
• Accuracy important!
• Design conditions
• Building shell load
• R, U value
• Internal load
• Ventilation load
• Infiltration
• Occupancy schedules
5. Heat Transfer
• Conduction
• Convection
• Radiation
• Resistance (R-Value)
• U = 1 / R
• Q = U x A x ∆T
U-Value is the rate of heat
flow in Btu/h through a one ft2
area when one side is 1o
F
warmer
6. The amount of solar
heat energy allowed to
pass through a window
Example: SHGC = 0.40
Allows 40% through and
turns 60% away
Solar Heat Gain Coefficient
9. Basic HVAC Equipment
• Fans / Blowers
• Furnace / Heating unit
• Filters
• Compressor
• Condensing units
• Evaporator (cooling coil)
• Control System
• Air Distribution System
10.
11. System Types and Common Terms
• Packaged Rooftop
Unit
• Split System
• Heat Pump
• Geothermal
• Air to Air
• Hydronic (water)
• PTAC / PTHP
Constant Volume
Variable Volume
Indoor Air Quality
Direct Expansion
14. Heat Pump
• Operate on simple
refrigeration cycle
• Reversing the cycle
provides heating
• Temperature limitations
• Air to air
• Water source
• Geothermal
• Lake coupled
16. Variable Air Volume
T T
Variable Speed
Return Fan
ReturnAir
Return Ducts
Zone Thermostat
Reheat Coil
VAV Box
Supply DuctsVariable Speed
Supply Fan
Filters
CoolCoilw/TempReset
HeatCoilw/Temp
Reset
HVAC-16
22. Economizers
Free cooling source: When available, use cool outdoor air
instead of mechanically cooled air.
55 o
F
80 o
F
Minimum supply
of outside air
Normal Operation
Outside air dampers are
positioned to provide the
minimum outside air
Economizer Operation
Outside air dampers are fully
open. Maximum outside air is
provided
80 o
F
55 o
F and
up
85%
outside
air
85%
exhaust
HVAC-22
23. Zoning and Economizers
• Economizers provide “free cooling”
when outdoor conditions are optimal
• Proper orientation & zoning yields
comfort & efficiency
N
S
W ECore
HVAC-23
24. Air Distribution
• Ductwork
– Metal
– Flexible
– Duct board
• Grilles, Louvers,
& Registers
• Dampers
– Shut off
– Fire
– Smoke
• Sealants
• Supports
28. Mechanical Dehumidification
Return air is mixed with ventilation air
Cold coil condenses moisture
Heat is added back (electric or gas) so that room air is not
over cooled- Reheat
Filter
30. Improved Ventilation Effectiveness
• Mechanically provide filtered and
dehumidified outdoor air to the
breathing space
• Vary ventilation based on the
number of occupants and process
loads - changes in occupancy can
be measured by CO2 sensors
• Consider designs that separate
ventilation and space conditioning
• Utilize heat recovery systems to
reduce system size and ventilation
energy costs
31. Improved Ventilation Effectiveness
• Effective mixing of
ventilation air within space
• Net positive pressure in the
southeast; exhaust from
appropriate spaces
• Provide clean outdoor air,
avoid:
– loading docks
– exhaust vents
– plumbing stacks
– waste collection
– stagnant water
32. Additional Information / Resources
• ASHRAE – The American Society of Heating,
Refrigerating and Air-Conditioning Engineers
– www.ashrae.org
• Geothermal heat pump consortium
www.geoexchange.org
• www.buildingscience.com
• www.energycodes.gov
Hinweis der Redaktion
1. Conduction is the transfer of heat through matter.
2. Convection is heat disbursement of heat through space, imagine ice at the top of the drink disbursing cold throughout the drink. (forced air systems)
3. Radiation is heat moving away in waves of energy from a heated object.
4. Consider the R-value of the structure.
5. Consider the U-value of windows.
Solar Heat Gain Coefficient (SHGC)
The glazing’s effectiveness in rejecting solar heat gain.
Part of a system for rating window performance used by the National Fenestration Rating Council (NFRC)
Gradually replacing shading coefficient (SC) in product literature and design standards convert SC to SHGC by multiplying the SC value by 0.87
Picture: heat gun view of a blower
Picture: Typical blower fans
An HVAC system consists of a
heating and/or cooling source,
a distribution system (e.g. ductwork or hot/chilled water piping) and
temperature controls.
Lake coupled systems are run to a sufficient body of water, and the coils are submerged in the water. The coils are wrapped in overlapping circles. The coils must be submerged at least 8ft to prevent freezing.
Hydronic – the oldest system, using steam or cold water driven through pipes to produce conditioning. This system often used in commercial buildings via radiators.
Optimum start – sensors on the outside of the building monitor the exterior temperature. The HVAC system starts up at the optimal time to ensure that the building temperature has reach the desired level at the time the occupants arrive.
DDC systems - Direct Digital Control – measure supply air temperature, mixed air temperature, return air temperature, outside air and outside humidity. This automated system economizes energy use by activity adjusting output in response to changing conditions.
Variable Speed Drives – control the ac power supplied to fans, blowers and other devices to optimize power usage during varying heating and cooling loads. By reducing the power supplied to a fan by 15 – 20% the system can reduce power usage by 30%
1. duct board is a fiber-glass based ductwork. It is self insulated with a R-value of 4.3 for a typical 1” thick board, reduces noise, reduce air leakage and is mold and condensation resistant.
2. Allow for dispersion of air from the HVAC system
3. Dampers allow for cutting off of air supply to unused rooms, fire dampers close in case of fire exposure to prevent the supply air from fueling the fire.
4. It is important to seal connections of components.
5. Properly spaced supports prevent the ductwork from sagging or falling. A sagging section of ductwork could cause connections to lose proper seal thereby lowering the efficiency of the entire system.
Plenum is the enclosed space. This slide is attempting to illustrate how poorly sealed soffits, ceilings and units contribute poor quality air into ventilation systems.
Left: Humidifier. This is a steam power humidifier. The coil inside (barely visible) heats the water in the reservoir and the steam enters the air flow. The humidifier in this picture is intended for heat pumps and furnaces.
Upper Right: Heat exchanger. The heat exchanger is comprised of tubes that are filed with a liquid, often water, a water-glycol solution, steam, or a refrigerant. The air is forced through the unit. The cooled or heated tubes affect the temperature of the air. Chillers are slightly different then heat exchangers. As the air travels through, latent moisture condenses on the chiller coils and the condensation must be collected and expedited to prevent mold growth.
Lower Right: This is a silencer. The supply air enters in one slot and exits through the other. Inside, the pathway is made of acoustical fill that helps silence the air as it travels. Typically they are bonded fibers to prevent the fibers from entering the airstream as it moves through the unit. These devices are used to silence the operations in areas where there is excess noise. These devices can be used in the supply runs and return runs.
This chart is showing that in the progression of mechanical ventilation with respect to the amount of air being forced through the system.
1. Ventilator
2. Vary ventilation – With more occupants, there is need for more fresh air to offset increased CO2 levels.
3. This allows for you to ventilate without running the conditioner, for example in times of pleasant outdoor temperatures such as the spring or fall.
4. Heat recovery systems are ventilation devices where the incoming air passes through a box and is affected by the exhausted air. The air flows are not mixed. The exhausted air is conditioned, and by passing through the device, 60 to 80 percent of the temperature is transferred to the incoming air. This preconditions the air before it enters the conditioning cycle.
* Note* - Open windows and bath fans are not adequate forms of ventilation!
1. This can be achieved by having the ventilation in conjunction with the duct systems, or through ceiling fans.
2. Positive pressure in the southeast to combat humid air infiltration. Do exhaust right next to an air intake, operable windows, or door ways.
3. These places all increase the likelihood of drawling in contaminated or undesirable air in to the building.