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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.

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SEMP/Energy Reliability HVAC Systems Overview

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  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. Basic Heat/Energy Transfer calculations continued: • Btu/hr = (500)(GPM)(water temp change) ** for hydronic heat/cool process

  9. 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)

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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)

  24. 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”

  25. 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

  26. ** 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

  27. 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

  28. Package Terminal Continued • Disadvantages: • low efficiency/high operating costs • high local noise both inside and outside room • short equipment life span

  29. 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

  30. 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

  31. 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)

  32. 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”

  33. 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

  34. 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 ?

  35. 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)

  36. 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

  37. 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

  38. 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

  39. 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

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