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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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semp energy reliability hvac systems overview
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
human thermal comfort
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
indoor air quality
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
indoor air quality4
Indoor Air Quality
  • “Sick Building Syndrome”:
    • Inadequate ventilation due to old code
    • Poor maintenance of HVAC equipment
      • standing water @ condensate pans
      • Bacteria growth @ cooling towers (Legionella)
    • “Tightness” of today’s buildings; non-operable windows
    • Outgassing of building materials
      • paint, furniture, carpeting. etc
indoor air quality5
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
definition of terms concepts
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
definition of terms concepts7
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

basic heat energy transfer calculations continued
Basic Heat/Energy Transfer calculations continued:
  • Btu/hr = (500)(GPM)(water temp change)

** for hydronic heat/cool process

definition of terms concepts9
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)
definition of terms concepts10
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
definition of terms concepts11
Definition of Terms/Concepts
  • Energy/Operating Costs:
    • BHP--> “brake” HP;
      • measure of actual fan/pump energy used
      • directly affects operating cost
    • kw/ton--> input power in kw

cooling capacity in tons

    • therms--> 1 therm = 100,000 btu
definition of terms concepts12
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
definition of terms concepts13
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

definition of terms concepts14
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

definition of terms concepts15
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
definition of terms concepts16
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
definition of terms concepts17
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
hvac system types
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
hvac system types19
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
hvac system types rooftop package units
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
hvac system types rooftop package units21
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
hvac system types rooftop package units22
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 EER’s: 8.5 for units up to 10 tons

8.2 for units between 10 -

25 tons

hvac system types rooftop package units23
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)

hvac system types rooftop package units24
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 @ 47 F ambient
    • minimum COP = 3.0 for Title 24
    • auxiliary electric heaters needed for cold winter A.M. and “defrost cycle”
hvac system types split system units
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
split system units continued
** 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
hvac system types package terminal ac heat pump units ptac
HVAC System Types**Package 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
package terminal continued
Package Terminal Continued
  • Disadvantages:
    • low efficiency/high operating costs
    • high local noise both inside and outside room
    • short equipment life span
hvac system types vav systems
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
hvac system types central plant
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--> 25-30 years
      • Greater flexibility in designing/selecting “engineered” components
      • Increased reliability of system
central plant hvac systems
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--> 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--> 72 F)

higher maintenance cost (cooling towers)

hvac building energy management systems
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”
hvac energy use management strategies
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
hvac energy use management strategies34
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 ?
hvac energy use management strategies35
HVAC: Energy Use & Management Strategies
  • Evaporative Pre-cooling
    • indirect vs. direct evaporative pre-cooling
  • Evaporative pads @ condenser coils
    • reduce condensing temperature for lower kw/ton
  • Evaporative Condensing Systems
    • (see supplemental Mammoth article)
hvac energy use management strategies36
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
energy reliability issues
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
energy reliability issues38
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
energy reliability issues39
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