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SEMP/Energy Reliability HVAC Systems Overview zPrimary purpose of HVAC for commercial/educational facilities- yHuman thermal comfort yIndoor Air Quality.

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Presentation on theme: "SEMP/Energy Reliability HVAC Systems Overview zPrimary purpose of HVAC for commercial/educational facilities- yHuman thermal comfort yIndoor Air Quality."— Presentation transcript:

1 SEMP/Energy Reliability HVAC Systems Overview zPrimary purpose of HVAC for commercial/educational facilities- yHuman thermal comfort yIndoor Air Quality zTerms/Definitions/Key Concepts zHVAC System Types zBuilding/Energy Management Strategies zEnergy Reliability Effect on HVAC

2 Human Thermal Comfort zCritical parameters: yTemperature-“hot vs. cold” yRelative humidity-“muggy vs. dry” yAir distribution-“drafty vs stale” zASHRAE Standards yAmerican Society of Heating, Refrigerating and Air conditioning Engineers( zOther concerns: yClothing level/Metabolic rate

3 Indoor Air Quality zUBC/UMC/Title 24 Ventilation rates: y“old” building code (prior to 1991) x5 CFM OSA per person/15 CFM recirc per person xgoal was to save energy during oil crisis y“current” building code x15 CFM per person or 0.15 CFM/sq. ft. yASHRAE recommendation x20 CFM per person for classroom/office space

4 Indoor Air Quality z“Sick Building Syndrome”: yInadequate ventilation due to old code yPoor maintenance of HVAC equipment xstanding condensate pans xBacteria cooling towers (Legionella) y“Tightness” of today’s buildings; non-operable windows yOutgassing of building materials xpaint, furniture, carpeting. etc

5 Indoor Air Quality yIAQ Solutions : y“bake-out” prior to occupancy ?? (not recommended by ASHRAE) y“ventilation purge”-ASHRAE yhire independent Air Quality Consultants xsampling of indoor air xlaboratory analysis of components xwritten report of findings

6 Definition of Terms/Concepts zHeat flow/heat transfer: yTemperature-“intensity” of heat xdry bulb temp vs. wet bulb temp yBtu-British thermal unit x“quantity” of heat yBtu/hour- rate of heat energy exchange yWatts1 watt = Btu/hour yTon1 ton = 12,000 Btu/hour yHP1 HP = 2,545 Btu/hour y 1 HP = 745 watts

7 Definition of Terms/Concepts zBasic Heat/Energy Transfer calculations: yBtu/hr = (1.08)(CFM)( dry bulb temp change) ** for “dry or sensible” heat/cool process ** yBtu/hr = (0.69)(CFM)(moisture change) ** for “wet or latent” cooling process ** yBtu/hr =(4.5)(CFM)( enthalpy change ) ** for “total” cooling process

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

9 Definition of Terms/Concepts zFluid Mechanics-(air/water flow) yVolume of airflow: (CFM, cubic ft./min. ) ySpeed of airflow:(FPM, feet per min. ) yPressure of airflow: (“w.g., “ H 2 O, inches of water gauge ) yVolume of waterflow: (GPM, gal./min. ) ySpeed of waterflow: (FPS, feet per second ) yPressure of waterflow: (ft. hd.; ft. of head, ft.of water )

10 Definition of Terms/Concepts zBasic air/water flow calculations: yCFM= (FPM) X (Area in Square Feet) yFor package units/comfort cooling 1 ton = 400 CFM y3 GPM/ton if water temp difference is 8 F y2.4 GPM/ton if water temp diff. is 10 F y2.0 GPM/ton if water temp diff. is 12 F y1.6 GPM/ton if water temp diff. is 15 F

11 Definition of Terms/Concepts zEnergy/Operating Costs: yBHP--> “brake” HP; xmeasure of actual fan/pump energy used xdirectly affects operating cost ykw/ton-->input power in kw cooling capacity in tons ytherms-->1 therm = 100,000 btu

12 Definition of Terms/Concepts zCommon Energy Efficiency Units: yEER/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” xEER used for 3 phase “commercial” equip. xSEER used for 1 phase residential condensing units

13 Definition of Terms/Concepts zCommon Energy Efficiency Units: yHEATING EQUIPMENT xAFUE-efficiency rating for furnaces/boilers Annual Fuel Utilization Efficiency AFUE= output btu/hour input btu/hour

14 Definition of Terms/Concepts zCommon Energy Efficiency Units: yHEATING EQUIPMENT xCOP-efficiency of heat pumps in heating mode Co-efficient Of Performance xCOP= output btu/hr input in watts

15 Definition of Terms/Concepts z“Title-24” Standards: ydictated by California Energy Comm. yBuilding Envelope constraints: xinsulation types and performance xglazing types and performance xinfiltration yLighting system constraints: xlighting levels (ft.candles, lumens, watts per sq. ft.) xfixture performance xuse of “day-lighting” and occupancy sensors

16 Definition of Terms/Concepts z“Title-24” Standards (cont.): yHVAC System constraints: xneed to justify sizing of proposed new equipment via load calculations xefficiency rating of heating/cooling equipment ( minimum levels of EER, AFUE, COP ) xestablishes standards for duct/pipe insulation xestablishes ventilation rates for building occupants

17 Definition of Terms/Concepts z“Title-24” Standards (cont.): xautomatic control and shutdown of equipment xneed for “air-side” economizers on larger systems xregulates use of electric resistance heat

18 HVAC System Types zAll-Air systems- (package/split AC units): yconstant volume, rooftop package or split system units yconstant volume, rooftop package or split system heat pumps yconstant volume, classroom package terminal heating/cooling units yvariable volume, rooftop package cooling/only units

19 HVAC System Types zAir/Water systems: ycentral plant chilled water systems ycentral plant hot water systems ycentral plant steam heating systems ywater-source heat pumps yair-cooled chilled water systems

20 HVAC System Types ** Rooftop Package Units** zWhy are these so Common ? yLow first cost yEasy to obtain/maintain ySimple to use/install/maintain yExcellent ventilation via air-side economizers

21 HVAC System Types ** Rooftop Package Units** zWhat are their shortcomings ? yHigh operating/maintenance cost y12-15 year lifespan yPre-packaged individual components y“Light commercial-grade” components

22 HVAC System Types ** Rooftop Package Units** zGas/Electric; Cooling/only; Heat Pumps yCooling 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 tons

23 HVAC System Types ** Rooftop Package Units** zHeating 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** z2)Package Heat Pumps- yheat is generated by refrigeration compressors yreversing valve changes function of evaporator and condenser yheat output is a function of OSA temperature yARI 47 F ambient yminimum COP = 3.0 for Title 24 yauxiliary electric heaters needed for cold winter A.M. and “defrost cycle”

25 HVAC System Types ** Split-System Units ** zWhy are these systems installed ? ySmaller outdoor equipment can be pad-mounted; no rooftop equipment required ycooling equipment can be added later ylocalized ducting systems take less attic space

26 ** Split-System Units ** Continued zDisadvantages yindoor equipment room required yindoor AH equipment difficult to maintain ylocal noise from AH equipment yexpensive refrigeration/condensate piping systems yventilation systems/ducting can be problematic

27 HVAC System Types **Package Terminal AC/Heat Pump Units (PTAC)** zWhy are these systems installed ? yLowest installed cost yNo ducting required ymultiple control zones yeasy replacement/access for maintenance

28 Package Terminal Continued zDisadvantages: ylow efficiency/high operating costs yhigh local noise both inside and outside room yshort equipment life span

29 HVAC System Types ** VAV Systems ** zCommon System types: yVaritrac/VVT- converts package unit to VAV yVAV cooling with constant volume perimeter heat yVAV with hot water reheat yDouble Duct VAV

30 HVAC System Types ** Central Plant ** zCentral Plant Systems: yWhy are these systems installed ? xLower ongoing operation/maintenance costs offset higher initial cost Life Cycle Cost/Present Worth Analysis xLonger lifespan of equipment-->25-30 years xGreater flexibility in designing/selecting “engineered” components xIncreased reliability of system

31 Central Plant HVAC Systems yAir-cooled vs. Water-cooled chillers xair-cooled:least expensive initial cost higher operating cost ( kw/ton) rated capacity based on T dry bulb (i.e. Sacramento--> 115 F minimum) xwater-cooled:higher initial cost lowest operating cost ( 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 zTypical System Features: yTime-of-day scheduling yOptimum start/stop yDuty Cycling yLoad Shedding zASHRAE “ECO” Guidelines y“Energy Conservation Opportunities”

33 HVAC: Energy Use & Management Strategies zDDC Controls: yaccess to “system information” yincreased monitoring capabilities for user y“smart” controls xoptimum start/stop; morning warm-up; night setback yremote contractor/technician access for troubleshooting

34 HVAC: Energy Use & Management Strategies zEconomizers: yutilize “free cooling” when it is available. yPackage units- advisable for systems 5 tons and larger for cost-effectiveness yenthalpy vs. dry bulb control zVariable Frequency Drives: yincreased reliability/efficiency yPG & E rebates ?

35 HVAC: Energy Use & Management Strategies zEvaporative Pre-cooling yindirect vs. direct evaporative pre-cooling zEvaporative condenser coils yreduce condensing temperature for lower kw/ton zEvaporative Condensing Systems y(see supplemental Mammoth article)

36 HVAC: Energy Use & Management Strategies zThermal Storage yuse of “off-peak” power rate structure to generate large volume of cooling capacity. ySmaller sized chilled water plants yCapital cost savings (rebates ?) yShift energy use vs. conserve energy yTake advantage of “cold-air” distribution systems

37 Energy Reliability Issues zPre-planning ydevelop list of “load-shedding” measures yestimate/measure value of individual load shedding item yprioritize items due to critical nature of loads xoffice/classroom cooling systems xcomputer rooms/file server rooms xtelephone equipment rooms xcommunications rooms zCommunicate with power supplier to establish “level” of Energy Emergency

38 Energy Reliability Issues zEmergency Load Shedding Strategies: yoptimize equipment operation thru good maintenance yRaise cooling setpoints yRaise chilled water supply temperatures yuse economizers if OSA temp is below room temp

39 Energy Reliability Issues zEmergency Load Shedding Strategies: yPre-cooling prior to emergency period yRotate equipment being turned off ykeep supply fans running for minimum ventilation ylockout refrigeration compressors yEnsure that ventilation/outside air dampers are at minimum position during hot weather


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