SEMP/Energy Reliability HVAC Systems Overview

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SEMP/Energy Reliability HVAC Systems Overview

• Primary purpose of HVAC for commercial/educational
  facilities-
• Human thermal comfort
• Indoor Air Quality
• Terms/Definitions/Key Concepts
• HVAC System Types
• Building/Energy Management Strategies
• Energy Reliability Effect on HVAC

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Human Thermal Comfort

• Critical parameters
• Temperature- hot vs. cold
• Relative humidity- muggy vs. dry
• Air distribution- drafty vs stale
• ASHRAE Standards
• American Society of Heating, Refrigerating and
  Air conditioning Engineers (www.ASHRAE.org)
• Other concerns
• Clothing level/Metabolic rate

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Indoor Air Quality

• UBC/UMC/Title 24 Ventilation rates
• old building code (prior to 1991)
• 5 CFM OSA per person/15 CFM recirc per person
• goal was to save energy during oil crisis
• current building code
• 15 CFM per person or 0.15 CFM/sq. ft.
• ASHRAE recommendation
• 20 CFM per person for classroom/office space

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Indoor Air Quality

• Sick Building Syndrome
• Inadequate ventilation due to old code
• Poor maintenance of HVAC equipment
• standing water _at_ condensate pans
• Bacteria growth _at_ cooling towers (Legionella)
• Tightness of todays buildings
  non-operable windows
• Outgassing of building materials
• paint, furniture, carpeting. etc

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Indoor Air Quality

• IAQ Solutions
• bake-out prior to occupancy ??
• (not recommended by ASHRAE)
• ventilation purge- ASHRAE
• hire independent Air Quality Consultants
• sampling of indoor air
• laboratory analysis of components
• written report of findings

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Definition of Terms/Concepts

• Heat flow/heat transfer
• Temperature- intensity of heat
• dry bulb temp vs. wet bulb temp
• Btu- British thermal unit
• quantity of heat
• Btu/hour- rate of heat energy exchange
• Watts 1 watt 3.414 Btu/hour
• Ton 1 ton 12,000 Btu/hour
• HP 1 HP 2,545 Btu/hour
• 1 HP 745 watts

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Definition of Terms/Concepts

• Basic Heat/Energy Transfer calculations
• Btu/hr (1.08)(CFM)(dry bulb temp change)
• for dry or sensible heat/cool process
• Btu/hr (0.69)(CFM)(moisture change)
• for wet or latent cooling process
• Btu/hr (4.5)(CFM)(enthalpy change)
• for total cooling process

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Basic Heat/Energy Transfer calculations
continued

• Btu/hr (500)(GPM)(water temp change)
• for hydronic heat/cool process

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Definition of Terms/Concepts

• Fluid Mechanics- (air/water flow)
• Volume of airflow (CFM, cubic ft./min.)
• Speed of airflow (FPM, feet per min.)
• Pressure of airflow (w.g., H2O, inches of
  water gauge)
• Volume of waterflow (GPM, gal./min.)
• Speed of waterflow (FPS, feet per second)
• Pressure of waterflow (ft. hd. ft. of head,
  ft.of water)

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Definition of Terms/Concepts

• Basic air/water flow calculations
• CFM (FPM) X (Area in Square Feet)
• For package units/comfort cooling
• 1 ton 400 CFM
• 3 GPM/ton if water temp difference is 8 F
• 2.4 GPM/ton if water temp diff. is 10 F
• 2.0 GPM/ton if water temp diff. is 12 F
• 1.6 GPM/ton if water temp diff. is 15 F

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Definition of Terms/Concepts

• Energy/Operating Costs
• BHP--gt brake HP
• measure of actual fan/pump energy used
• directly affects operating cost
• kw/ton--gt input power in kw
• cooling capacity in tons
• therms--gt 1 therm 100,000 btu

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Definition of Terms/Concepts

• Common Energy Efficiency Units
• EER/SEER- efficiency rating for cooling equip
  Energy Efficiency Ratio
• Seasonal Energy Efficiency Ratio
• EER or SEER cooling capacity in btu/hour
• input power used in watts
• EER used for 3 phase commercial equip.
• SEER used for 1 phase residential condensing
  units

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Definition of Terms/Concepts

• Common Energy Efficiency Units
• HEATING EQUIPMENT
• AFUE- efficiency rating for furnaces/boilers
• Annual Fuel Utilization Efficiency
• AFUE output btu/hour
• input btu/hour

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Definition of Terms/Concepts

• Common Energy Efficiency Units
• HEATING EQUIPMENT
• COP- efficiency of heat pumps in heating mode
• Co-efficient Of Performance
• COP output btu/hr
• input in watts

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Definition of Terms/Concepts

• Title-24 Standards
• dictated by California Energy Comm.
• Building Envelope constraints
• insulation types and performance
• glazing types and performance
• infiltration
• Lighting system constraints
• lighting levels (ft.candles, lumens, watts per
  sq. ft.)
• fixture performance
• use of day-lighting and occupancy sensors

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Definition of Terms/Concepts

• Title-24 Standards (cont.)
• HVAC System constraints
• need to justify sizing of proposed new equipment
  via load calculations
• efficiency rating of heating/cooling equipment
  (minimum levels of EER, AFUE, COP)
• establishes standards for duct/pipe insulation
• establishes ventilation rates for building
  occupants

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Definition of Terms/Concepts

• Title-24 Standards (cont.)
• automatic control and shutdown of equipment
• need for air-side economizers on larger systems
• regulates use of electric resistance heat

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HVAC System Types

• All-Air systems- (package/split AC units)
• constant volume, rooftop package or split system
  units
• constant volume, rooftop package or split system
  heat pumps
• constant volume, classroom package terminal
  heating/cooling units
• variable volume, rooftop package cooling/only
  units

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HVAC System Types

• Air/Water systems
• central plant chilled water systems
• central plant hot water systems
• central plant steam heating systems
• water-source heat pumps
• air-cooled chilled water systems

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HVAC System Types Rooftop Package Units

• Why are these so Common ?
• Low first cost
• Easy to obtain/maintain
• Simple to use/install/maintain
• Excellent ventilation via air-side economizers

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HVAC System Types Rooftop Package Units

• What are their shortcomings ?
• High operating/maintenance cost
• 12-15 year lifespan
• Pre-packaged individual components
• Light commercial-grade components

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HVAC System Types Rooftop Package Units

• Gas/Electric Cooling/only Heat Pumps
• Cooling capacities
• 1 ton 400 CFM (/- 20 flexibility)
• unit capacity total capacity NOT sensible
  capacity
• sensible cooling capacity 70-80 of total
• capacity
• ARI ratings 95F ambient, 80F edb, 67F ewb
• minimum EERs 8.5 for units up to 10 tons
• 8.2 for units between 10 -
• 
  25 tons

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HVAC System Types 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(AFUE) 80
• Typically low heat models used in California
• Aluminized steel heat exchangers (SS as
• option)

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HVAC System Types Rooftop Package Units

• 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
• ARI ratings _at_ 47 F ambient
• minimum COP 3.0 for Title 24
• auxiliary electric heaters needed for cold winter
  A.M. and defrost cycle

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HVAC System Types Split-System Units

• Why are these systems installed ?
• Smaller outdoor equipment can be pad-mounted no
  rooftop equipment required
• cooling equipment can be added later
• localized ducting systems take less attic space

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Split-System Units Continued

• Disadvantages
• indoor equipment room required
• indoor AH equipment difficult to maintain
• local noise from AH equipment
• expensive refrigeration/condensate piping systems
• ventilation systems/ducting can be problematic

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HVAC System TypesPackage Terminal AC/Heat
Pump Units (PTAC)

• Why are these systems installed ?
• Lowest installed cost
• No ducting required
• multiple control zones
• easy replacement/access for maintenance

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Package Terminal Continued

• Disadvantages
• low efficiency/high operating costs
• high local noise both inside and outside room
• short equipment life span

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HVAC System Types VAV Systems

• Common System types
• Varitrac/VVT- converts package unit to VAV
• VAV cooling with constant volume perimeter heat
• VAV with hot water reheat
• Double Duct VAV

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HVAC System Types Central Plant

• Central Plant Systems
• Why are these systems installed ?
• Lower ongoing operation/maintenance costs offset
  higher initial cost
• Life Cycle Cost/Present Worth Analysis
• Longer lifespan of equipment--gt 25-30 years
• Greater flexibility in designing/selecting
  engineered components
• Increased reliability of system

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Central Plant HVAC Systems

• Air-cooled vs. Water-cooled chillers
• air-cooled least expensive initial cost
• higher operating cost (1.2-1.6 kw/ton)
• rated capacity based on T dry bulb
• (i.e. Sacramento--gt 115 F minimum)
• water-cooled higher initial cost
• lowest operating cost (0.5-0.8 kw/ton)
• rated capacity based on T wet bulb
• (i.e. Sacramento--gt 72 F)
• higher maintenance cost (cooling towers)

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HVAC Building/Energy Management Systems

• Typical System Features
• Time-of-day scheduling
• Optimum start/stop
• Duty Cycling
• Load Shedding
• ASHRAE ECO Guidelines
• Energy Conservation Opportunities

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HVAC Energy Use Management Strategies

• DDC Controls
• access to system information
• increased monitoring capabilities for user
• smart controls
• optimum start/stop morning warm-up night
  setback
• remote contractor/technician access for
  troubleshooting

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HVAC Energy Use Management Strategies

• Economizers
• utilize free cooling when it is available.
• Package units- advisable for systems 5 tons and
  larger for cost-effectiveness
• enthalpy vs. dry bulb control
• Variable Frequency Drives
• increased reliability/efficiency
• PG E rebates ?

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HVAC Energy Use Management Strategies

• Evaporative Pre-cooling
• indirect vs. direct evaporative pre-cooling
• Evaporative pads _at_ condenser coils
• reduce condensing temperature for lower kw/ton
• Evaporative Condensing Systems
• (see supplemental Mammoth article)

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HVAC Energy Use Management Strategies

• Thermal Storage
• use of off-peak power rate structure to
  generate large volume of cooling capacity.
• Smaller sized chilled water plants
• Capital cost savings (rebates ?)
• Shift energy use vs. conserve energy
• Take advantage of cold-air distribution systems

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Energy Reliability Issues

• Pre-planning
• develop list of load-shedding measures
• estimate/measure value of individual load
  shedding item
• prioritize items due to critical nature of loads
• office/classroom cooling systems
• computer rooms/file server rooms
• telephone equipment rooms
• communications rooms
• Communicate with power supplier to establish
  level of Energy Emergency

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Energy Reliability Issues

• Emergency Load Shedding Strategies
• optimize equipment operation thru good
  maintenance
• Raise cooling setpoints
• Raise chilled water supply temperatures
• use economizers if OSA temp is below room temp

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Energy Reliability Issues

• Emergency Load Shedding Strategies
• Pre-cooling prior to emergency period
• Rotate equipment being turned off
• keep supply fans running for minimum ventilation
• lockout refrigeration compressors
• Ensure that ventilation/outside air dampers are
  at minimum position during hot weather