HVAC “Basic Science”- System Capacity
• Btu/hour, btu/h, b/h, btuh…. btu ??
• 1 MBH = 1000 btu/hour
• 1 KBH = 1000 btu/hour
• 1 ton of cooling= 12,000 btu/hour
• 1 watt = 3.414 btu/hour
• 1 kilowatt = 1000 watts = 3,414 btu/hour
• 1 HP = 746 watt = 2,545 btu/hour
1
HVAC Airflow- Duct and Component Sizing
• CFM- volume of airflow; cubic feet/minute
• FPM- velocity/speed of airflow; feet/minute
• AREA- duct size in square feet
CFM = FPM X AREA
FPM = CFM/AREA
AREA= CFM/FPM
2
Indoor Environmental Quality (IEQ)
Title 24- Minimum Ventilation Requirements
• Applies to “normally occupied” spaces
• Natural ventilation-
• 20’ maximum distance from occupied space
to window/wall opening
• 1 sq ft of opening for 20 sq ft of floor area
(NOTE: “free area” of opening)
• Mechanical ventilation
• EF’s and makeup air
• Required for areas with moisture (showers)
3
IEQ- Ventilation Systems
Natural “Passive” Ventilation
• motorized clerestory windows
• filtered low-wall intake louvers
Mechanical Ventilation
• 15 CFM per person OR 0.15 CFM/sq ft
• Air change calculation- # AC/hour
CFM req’d = (Room volume- FT3)(# AC/hour)
60
4
Passive Ventilation- CHPS project
5
IEQ- Economizers
• Provide “free” cooling for space if OSA temp is
below space temperature (i.e. 72F)
• T24 requirement for systems > 2,500 CFM and
75 MBH (appx 6.25 tons)
• BEWARE!! Motorized dampers need maintenance
• Where does all this OSA go?…building pressure
problem!
• Power exhaust
• Barometric relief
6
Economizer (rooftop package unit)
7
Economizer (rooftop package unit)
8
Economizer (split system)
9
IEQ- Ventilation Methods
Demand Controlled Ventilation (DCV)
• Mandatory for high occupancy zones (less than
40 ft2 per person density)
• CO2 sensor controls economizer dampers
• Classrooms are exempted (but still worth
considering!)
Displacement Ventilation
• Underfloor vs. low-wall ducts
10
Displacement Ventilation
11
IEQ/Acoustics
• Velocity (FPM)
• Damper locations: duct MVD’s vs. register
OBD’s
• Sound traps vs. lined rectangular duct
• CHPS requirements
• RC/NC levels
12
HVAC System Types
• Energy Recovery Ventilators (ERV’s)
• Evaporative Cooling (Direct vs. Indirect)
• Heating systems
• Refrigeration Cycle overview
• Refrigerant types (CFC vs non-CFC)
• Split systems (furnaces/fan-coils with CU’s)
• Package units (gas/electrics and heat pumps
• Geothermal heat pumps
13
Energy Recovery Ventilators (ERV’s)
14
Energy Recovery Ventilators (ERV’s)
15
ERVs (how they work)
16
ERVs (how they work)
17
ERV’s- Economics/Simple Payback
18
Heating Equipment and Systems
Residential Furnaces-
Standard efficiency furnaces 80% AFUE
AFUE: (Annual Fuel Utilization Efficiency) = output capacity(btu/hr)
input capacity (btu/hr)
High efficiency “condensing furnaces” 92-95% AFUE
PVC flue material
Condensate neutralizers on condensate drains?
Configuration: Downflow/Upflow/Horizontal flow
R.O.T. sizing = 50 btu/hr per square foot of floor area
Evaporative Cooling
(no refrigeration/mechanical cooling)
“Direct” (swamp coolers)
• Evaporated water in contact with air
• Useful in dry climates
“Indirect”
• Evaporated water NOT in contact with air
• Large/heavy units
Combo “Direct/Indirect” (IDEC units)
20
Basic Refrigeration Cycle Components
• Refrigerant- “magic fluid”
• Compressor- increases refrigerant pressure and
temperature; performs work
• Condenser coil- Heat rejection
• Refrigerant metering device (TXV or capillary
tube)
• Evaporator coil- delivers cooling to space
• Refrigerant piping- suction/liquid/hot gas lines
21
Refrigerant types
CFC’s (chlorinated fluorocarbons)---BAD!
• R-11 or R-12
• Effect on earth’s ozone layer/global warming
HCFC’s (hydrogenated CFC)---BETTER!!
• R-22
• Phased out by 2020
New Refrigerants- R-134a; R-410a; “Puron” ---
BEST!!!
22
Split System Cooling/Heat Pumps
• Furnace compatibility with “cased cooling
coil”
• Outdoor condensing units
SEER- “seasonal” Energy Efficiency Ratio
Power requirement
• Refrigeration linesets
• Multi-zone “ductless” systems
• Evaporator coil condensate piping and IAQ
23
Rooftop Package Units
• Typical System Types:
Package “cooling/only” units
Package “gas/electric” units
Package heat pumps
• All above are “air-cooled”
Typically rated @ 95 F condensing temp
Watch out for elevated roof temperature
Good air circulation is a must !
Rooftop Package Units
• Cooling capacities
1 ton = 12,000 btu/hour
1 ton = 400 CFM (+/- 20% flexibility)
unit capacity = total capacity NOT sensible capacity
(rated @ 95F ambient, 80F edb, 67F ewb)
sensible cooling capacity 70-80% of total
latent capacity provided >what is needed on West coast
gross capacity does NOT include deduction for fan heat
EER (Energy Efficiency Ratio)= btu/hr output
KW input
Rooftop Package Units
• Heating Capacities:
1) Gas/electric units-
Input capacity (1 MBH = 1000 btu/hr)
Output capacity (1 MBH = 1000 btu/hr)
Efficiency = output MBH/input MBH
Title 24 minimum efficiency= 80%
Typically “low heat” models used in California
“Aluminized steel” heat exchangers (SS as option)
Rooftop Package Units
• Heating capacity (cont.):
2) Package Heat Pumps-
heat is generated by refrigeration compressors
reversing valve changes function of evaporator
and condenser
heat output is a function of OSA temperature
COP (Coefficient Of Performance)
auxiliary electric heaters needed for cold winter
A.M.and defrost cycle
Rooftop Package Units
Advantages: Disadvantages:
• limited flexibility to
• inexpensive select/change components
• fast delivery/installation • higher operating &
• simple to design and operate maintenance cost than
“central systems”
• “air-side”economizers • not good for tight
• ratings from manufacturers temperature/RH control
are certified • not good for high % of OSA
• if system fails, only 1 zone • looks not appealing
affected • filtration options limited
• easy to meter for utility billing • fan performance limited
(particularly static pressure)
purposes • shorter equipment life
• installed on roof for easy
maintenance
