Building Systems and Performance: an Introduction to Building Operator Certification Lesson 17: Maintaining for Performance and Energy Calculations

Transcription

1 Building Systems and Performance: an Introduction to Building Operator Certification Lesson 17: Maintaining for Performance and Energy Calculations CUNY Institute for Urban Systems Building Performance Lab

2 2 Agenda for Lesson 17 Topic 1: Maintaining Performance Topic 2: Energy Calculations

3 3 Topic 1: Maintaining Performance O&M with a focus on achieving energy savings O & M strategies to achieve energy reduction in systems: Lighting, HVAC, Boilers, Heating, Cooling New York City has set targets to reduce energy usage (PlaNYC): Reduce by 30% by the year 2017 Buildings comprise % of the City s total energy usage Benchmarking is required by Local Law 84 Reductions of 10% in energy use possible with little or no cost.

4 Energy & O&M 4 Biggest Energy Users are Lights & HVAC

5 Energy-Related O&M The Top Combustion tune-up & minimize cycling 2. Refrigerant charge and condenser temperature 3. Clean heat exchangers 4. Damper operation, esp OA 5. Belts - replace, adjust 6. Leaks - steam, water, air, compressed air 7. Steam traps 8. Distribution balance 9. Schedules (on/off), settings and resets 10. Sensor calibration

6 Energy & O&M 6 Reduce Lighting Loads: Lighting is 33% of Energy Costs Check lighting levels to reduce overlit areas Adjust lighting controls to match occupancy Use daylighting whenever possible Clean luminaires, replace discolored lenses and diffusers Maintain reflective room surfaces

7 Energy & O&M 7 Use Lighting Controls Infrared Sensors Ultrasonic Sensors Dual Technology: Infrared and Micro-phonic Application Savings Offices (Private) 25-50% Classrooms 20-25% Rest Rooms 30-75% Corridors 30-40% Storage Areas 45-65% Cafeterias 45-65% Conference Rooms 45-65%

8 HVAC Maintenance Energy & O&M Clean heat exchanger surfaces: Allow air to freely flow around heat exchangers Adjust burner on boiler for optimum efficiency Replace air filters regularly Seal ductwork leaks Calibrate and test all control devices on a regular basis Keep good system equipment records Keep O&M manuals & instructions accessible 8

9 Energy & O&M 9 Plug Loads- Savings opportunities! Lights Peripherals (printers, scanners, etc.) Space Heaters Energy Star computers, monitors, etc. The importance of policies and organizational practices for your facility. For necessary equipment, consider upgrading to energy efficient models.

10 Monitoring Your System s Performance 10 The basic operation of the HVAC Systems in your building: How do you know if your systems are operating properly?

11 Key Conditions to Look for in Performance 11 Supply air temperature from AHU, supply air temp to cool water to warm Discharge air temp after the reheat coil, if possible to monitor (if not available, monitor the reheat valve position) Electrical heater stage or on/off status Zone air temperature & occupancy mode VAV damper position Outdoor air temperature reading from outdoor air sensor No night time setback Overcooling or overheating No use of temperature reset for supply air Certain zones (corner offices, etc.) driving air handler operation Some zones are out of control, oscillating between heating and cooling Significant reheat for interior zone terminal box during the occupied hours -significant reheat during summer cooling season for exterior zones

12 Zones to watch for common problems 12 Zones with comfort complaints Office (space) no longer occupied as originally designed Interior zones with very little cooling load (small offices) Exterior zones with reheat during cooling season Zones with high minimum airflow settings (> 35% for example)

13 Operational Problems The Top 4 Savings Opportunities Scheduling (includes equipment staging, zoning) 2. Sensor Error Thermostats and controls 3. Simultaneous Heating & Cooling 4. Outside Air usage Schedule When the equipment operates Efficiency How the equipment operates Source: Better Bricks

14 14 Green Control Strategies - Scheduling Shut off systems / use deep setbacks whenever possible Night and holiday unoccupied schedules- Weekend schedules- refrain from starting up systems for occasional weekend/nighttime use Use bypass buttons Develop a schedule for each zone Identify the spaces with low use Auditorium, class rooms, conference rooms Unoccupied mode a major cost saver- make sure it s enabled; simple to track, administer and measure! Off hour cleaning crews Working at night with all HVAC running, all fresh air open & lights on Is this required? Do not restart too early Use a startup schedule based on building needs Simple controls can achieve big savings Occupancy Sensors (Lighting & HVAC) Smart Thermostats these learn the warm-up patterns

15 Green Control Strategies If needs to run 24/7, can it be set back during the unoccupied hours? Reset Schedules AHU Discharge Air Temp Hot Water Temp Chilled Water Temp Static Pressure Alarm valve leak by Temperature policy Demand Ventilation Control. IAQ sampling technology Set point coordination No simultaneous heating and cooling Maximize Free Cooling Sensor Calibration, Damper Maintenance Enthalpy calculations 15

16 Green Control Strategies- Air Side Economizer Look for these off-normal operating conditions: 16 Outdoor-air dampers open at unusual times of day or under unusual outdoor temperature conditions Outdoor-air dampers not open to economizer under favorable conditions (outdoor-air temperature between 40 F and 60 F) Outdoor-air damper not closing to minimum position for freeze prevention when outdoor temperature is less than about 35 F Outdoor-air damper position and chilled-water valve position (%open). The outside-air damper should be wide open before mechanical cooling is used.

17 Green Control Strategies-Economizer 17 Potential issues to identify Incorrect economizer operation numerous causes Incorrect control strategy Stuck dampers Disconnected or damaged linkages Failed actuator Disconnected wires Failed, uncalibrated or miscalibrated sensors Blockage in dampers or pest/bird screens

18 Topic 2: Energy Calculations 18 How to calculate energy savings? - Understand how energy is used by building systems and equipment - Use spreadsheets to calculate savings for improvements - Decide between two or more alternative projects choices - Estimate post-retrofit energy budgets, relate calculations to energy use histories

19 Energy Calculations 19 Energy calculations generally take the form of: Equipment energy use (flow rate) X operating hrs. (time) = energy use Equipment energy use can be taken from the equipment nameplate- this provides rated energy use. In some cases, this will be quite accurate but in other cases (under-loaded motors, dimmed lights, or modulating burners, etc.) it may not be. In such cases, energy use should be measured. Operating hours are often estimated - but measurement is often better.

20 Energy Calculations 20 We can calculate energy of an existing condition- by varying equipment rating and/or the operating hours, a future retrofitted condition. Taking the difference between these two states provides us with savings from the retrofit. All energy savings calculations take basically the same format: Energy Savings = Energy used before Energy used after and $ Saved = Energy saved x $/unit of energy ($/kwh, $/therm, $/gallon)

21 21 Energy Calculations: Lighting Changes One of the most common energy conservation projects is a lighting system upgrade. Such a project might involve an upgrade from T-12 lamps and magnetic ballasts to T-8 lamps and electronic ballasts. For a lighting system upgrade, we need to know 4 things: 1. Wattage of existing T-12 lamp fixture and ballast combination. 2. Wattage of the proposed T-8 lamp and ballast combination. 3. Total number of fixtures involved. 4. Total number of hours lighting is on in the retrofitted areas (simple or complicated, especially when hours vary in different spaces)

22 Energy Calculations: Lighting Changes 22 A lighting system upgrade: To obtain the number of fixtures, we would inventory the area to be retrofitted and count the number of fixtures. Lets say we count 50 fixtures and we know that the space operates 10 hours per day, 5 days per week, 52 weeks per year. Next, obtain the Watts/fixture of the existing T-12/ballast combination. Either open one of the fixtures and note the wattage and number of the lamps and the ballast or locate the lamp/ballast Wattage combination from reference guide, contractor or manufacturer. Let say that the fixture being replaced has two F48T12 lamps and one standard magnetic ballast with a total of 81 Watts per fixture.

23 23 Energy Calculations: Lighting changes A lighting system upgrade: finally, we need the Watts/fixture of the replacement fixture. Obtained as before, from contractor, manufacturer or similar reference. Let say the replacement fixture has two F30T8 lamps with a total of 59 Watts per fixture. We can now calculate the energy savings for the project. Watts saved = (Watts of Existing System Watts of Proposed System) x the number of fixtures = (103W/fixture 59W/fixture) x 50 fixtures = 44W/fixture x 50 fixture = 2,200W saved Since we typically think in terms of kilowatts (1,000 Watts), = 2,200W* 1 kw/ 1,000 W = 2.2Kw saved

24 Energy Calculations: Lighting Changes 24 We can now calculate the energy savings for the project. Energy savings = 2.2Kw x 10 hours/day * 5 days/week * 52 weeks/year = 5,720 kwh/year saved We need to know the energy rate ($/kwh) the facility pays in order to calculate the cost savings for this project. Average $/kwh = Total Annual Electricity Bill ($) / number of kwh used in the year. i.e. - $80,000/400,000 kwh = $0.20 per kwh Savings per year = 5,720 kwh x $0.20/kWh = $1,144

25 Energy Calculations: Lighting Changes 25 Once you are comfortable with these steps, you can combine them into one equation to get the total energy saved in a year for the project: (W pre W post ) x # of fixtures x operating hours per yr/ 1000 = kw saved per year For example: (103W/fix 59W/fix) x 50 fixtures x 2,600 hrs/yr / 1000 = 5,720 kwh $0.20 per kwh= 5,720 kwh x $0.20 = $1, per year saved

26 26 Energy Calculations: Lighting changes The project is to replace 50 compact fluorescent exit signs each using 12 Watts with 50 LED exit signs each with 2 LEDs for a total of 3 Watts per fixture. Calculate the savings in kw, kwh, and $ based on $.020 per kwh, Above is a simple spreadsheet you can develop and use to calculate the savings offered by this project. The yellow highlighted cells are equations that use data you can input in the non-highlighted cells. Total Watts = Watts/fixture * Number of Fixtures Watt Hours = Total Watts * Hours kwh = Watt Hours / 1000 Watts per kilowatt Annual cost = kwh * $0.20/kWh

27 Energy Calculations: Lighting changes 27 The project is to replace 50 compact fluorescent exit signs each using 12 Watts with 50 LED exit signs each with 2 LEDs for a total of 3 Watts per fixture. Calculate the savings in kw, kwh, and $ based on $.020 per kwh, Fixture Type W/fixture Number of Fixture Total Watts Hours Watt Hours kwh Annual $0.20/kWh Exisitng Exit CFL ,256,000 5,256 $ 1,051 Proposed Exit LED 2 lamp ,314,000 1,314 $ 263 Savings 450 3,942,000 3,942 $ 788

28 Energy Calculations: Lighting changes 28 Lighting power density is another required lighting calculation. The lighting power density (LPD) is the Watts per square foot for a space. Notice that LPD does not consider operating hours. Recall from the Lighting Technology lesson that LPD is how energy codes address lighting, setting maximum LPD allowable for spaces of various types.

29 Energy Calculations: Lighting Changes We can calculate the LPD before and after the project used in the previous example. Let say the office space in the previous example has an area of 3,600 SF. The existing case has 50 T12 fixtures, each using 80 Watts, or 4,000 Watts. Existing LPD = 4,000W/3,600 sf = 1.11 Watts/sf 29 The proposed case has 50 T8 fixtures, each using 60 Watts, or 3,000 Watts. Proposed LPD = 3,000W/3,600 SF = 0.83 Watts/sf If we only had the before and after LPD values, we d calculate project savings as: Savings = (LPD before LPD after ) x sf = (1.11 W/sf 0.83 W/sf) x 3,600 SF = 1,000 Watts or 1kW If we assume an average energy cost of $0.20 per kwh with lighting on 12/hrs/day, five days per week, savings equal: kwh = kw x hours = 1kW x 12 hours/day x 5 days/week x 52 weeks/year = 1kW x 3,120hours = 3,120 kwh per year saved At $0.20 per kwh, 3,120 kwh x $0.20/ kwh = $624 saved per year (or, if we only know the existing Watts and code requirement, we can calculate what we would have to reduce to comply with the Code.)

30 30 Energy Calculations: Measure Interaction Let s see what happens when we introduce a second common lighting project opportunity into the project scenario: Occupancy Sensors Building bathroom lights on continually The building has 10 floors with 2 bathrooms / floor (M/F) Each bathroom has 3 2 F40 / bathroom at 88 watts / fixture Two recommendations: (1) Change all fixtures to 2 F32 T5 at 70 Watts/ fixture (2) Install occupancy sensors (2 per bathroom) to reduce operating hours from 8,760/yr to 2,500/yr

31 Energy Calculations: lighting changes, measure 31 interaction and avoiding double counting When implementing multiple energy efficiency projects in the same space, take care not to over estimate savings due to double counting: some measures interact with other measures and therefore the sum of the two measures together can be less than if the two measures were considered individually. For example, let s look at two lighting project opportunities that commonly occur together: fixture upgrades and occupancy sensors. If we are turning off the lights with the occupancy sensors, then the operating hours and savings of the fixture retrofit will be reduced. Conversely, with higher efficiency fixtures in place, the savings from the occupancy sensors will be less than with less efficient fixtures. Let s look at how this works out numerically.

32 32 Energy Calculations: Lighting changes & double counting Using the spreadsheet created earlier, by installing occupancy sensors on the existing fixtures our savings calculations look like this: Occupancy sensor w/ existing fixtures Fixture Type W/fixture Number of Fixture Total Watts Hours Watt Hours kwh Annual $0.20/kWh Exisitng F40T ,280 8,760 46,252,800 46,253 $ 9,251 Proposed F40T8 w/ occ sensors ,280 2,600 13,728,000 13,728 $ 2,746 Savings - 32,524,800 32,525 $ 6,505 Installing occupancy sensors on the old fixtures will save 32,525 kwh or $6,505 per year.

33 Energy Calculations: Lighting changes and double counting 33 If, instead, we change out the fixtures first, our calculation looks like this: Fixture replacement Fixture Type W/fixture Number of Fixture Total Watts Hours Watt Hours kwh Upgrading to new fixtures will save 9,461 kwh or $1,892 per year. Combining the two project savings individually would yields: 32,525 kwh + 9,461 kwh = 41,986 kwh $6, ,892 = $8,397 BUT BE CAREFUL Annual $0.20/kWh Exisitng F40T ,280 8,760 46,252,800 46,253 $ 9,251 Proposed F32T ,200 8,760 36,792,000 36,792 $ 7,358 Savings 1,080 9,460,800 9,461 $ 1,892

34 34 Energy Calculations: Lighting changes and double counting HOWEVER, if both projects are implemented (occupancy sensors are installed and the fixtures replaced), our calculation would look like this: Occupancy Sensors & Fixture Replacement Number Annual of Total Fixture Type W/fixture Fixture Watts Hours Watt Hours kwh $0.20/kWh Exisitng F40T ,280 8,760 46,252,800 46,253 $ 9,251 F32T5 w/ occ Proposed sensors ,200 2,600 10,920,000 10,920 $ 2,184 Savings 1,080 35,332,800 35,333 $ 7,067 Doing both projects will save a combined 35,333 kwh or $7,067 per year. If we compare the two individual project savings calculations with the combined project savings calculation, we see that the individual projects save more than they will when combined : 41,986 kwh - 35,333 kwh = 6,653 kwh $8,397 - $7,066 = $1,331 An overstatement of savings by 6,653 kwh or $1,331. We don t want to cheat ourselves by being overly conservative but we would rather exceed an underestimate of savings than Fall short of an over-estimate!

35 Energy Calculations: Heating System improvements 35 Heating energy can be improved by changes to the building envelope (insulation or reduction of outside air infiltration) or by heating system improvements. The former are calculated by pre/post calculation of the heat loss formula U x dt or by ACH x V x dt, where we change the conductance value of the wall (U) or the ACH (Air Changes per Hour,) much as we would change the wattage of a lighting fixture. Degree-days usually represent the amount of heating to be done, equivalent to operating hours. We ll work through a simple ventilation reduction example. Improvements to heating systems are usually calculated a bit differently, using changes in efficiency applied to actual energy use. We ll work through several examples of this kind.

36 Energy Calculation: Infiltration/Ventilation Reduction 36 Let s say we determine we need 6,000 cfm of outside air (OA) supply to satisfy code requirements in our building but based on measurements taken the actual outside air being supplied is 10,000 cfm. Every extra cfm of OA requires more energy to heat. The energy needed to heat air to 68 o F 20 o F OA temperature is calculated as Q = cfm x (0.075lb/cfm x 0.24 Btu/lb/ o F x (60 min/hr) x dt = cfm x 1.08 x dt So the heating energy needed to heat the extra 4,000 cfm of OA is Q = 4,000 cfm x 1.08 x (68 20) = 4,000 x 1.08 x 48 = 207,360 Btuh. But this only tells us part of what we need. (Note that this is the extra heat required for every hour of system operation.)

37 Energy Calculation: Infiltration/Ventilation Reduction 37 To understand what the impact will be to the energy bill, we must also take into account the heating system efficiency because we have only calculated the amount of extra heat we need and not the amount of fuel necessary to provide it. So if our boiler is 80% efficient, then Q = 207,360 Btuh/0.80 = 259,200 Btuh required for the extra OA or 1.85 gallons of #2 oil at 140,000 Btu per gallon. At $3.50 per gallon, $6.48 per hour extra (to project out savings we would multiply this rate by hours that both our heating and ventilating system are operating)

38 Energy Calculations: Boilers & Heating We can build up energy use at a boiler from its firing rate and operating hours. This can be tricky since a boiler is cycling on and off and often modulating its firing rate. We ll do some calculation varying these factors. 38 But more commonly we talk about boiler plant improvement in terms of efficiency change. If we want to quantify this kind of improvement we have to apply it to the annual fuel use. And we have to be careful that we are applying it to the right portion of fuel use! For example, an improvement to the summer efficiency for hot water production should be applied only to the summer fuel use. Let s work through an example of this kind of improvement.

39 Energy Calculations: Heating System Improvements How about a boiler project that tunes, improves controls and repairs insulation. Let s estimate that these steps improves the boiler efficiency form 70% to 80%. For a 500 kbtu/ hr boiler this results in a savings of 500kBtuh/0.70 = kbtuh and 500kBtuh/0.80 = kbtuh kbtuh kbtuh = kbtu savings per hour 39 Alternatively, if we knew the annual fuel consumption of the boiler was 8,600 therms and improving the boiler insulation will improve its operating efficiency from 70% to 80% provides ( ) / 0.8 = or 12.5%. So 8,600 therms/yr x = 1,075 therms saved $3.00 per therm reveals savings of: 1,075 therms x $3.00 = $3,225 saved per year

40 Energy Calculations: Night Setback 40 Another common heating system efficiency opportunity installing (and using) a thermostat with night time set back. Let s say our building maintains of 75 o F inside temperature day and night. What would the savings be if the interior thermostat was set back from 75 o F to 65 o F at night during unoccupied hours? First we need to the annual energy required to heat the building. Let say the building uses 120,000 gallons of No.2 fuel oil/year for heating. (Remember, if the building uses fuel oil for other purposes, say to heat water or fuel generators, that amount must be deducted from the annual fuel oil total.) Fuel saved = Annual fuel used x % setback hours (unoccupied) x % temp setback The percent reduction of the night set is: % night set reduction = (T before T after ) / T before = (75 65) / 75 = =13.3%

41 Energy Calculations: Night Setback 41 The number of hours the building is currently heated is: 26 weeks x 7 days/wk x 24 hours/day = 4,368 hours. If the building is unoccupied from 7 pm to 7 am, Monday through Friday and all weekend hours, the unoccupied hours are calculated as: 26 wks x (5 wkdays x 12 hrs + 48 wkend hrs) = 26 wks x 108 hrs/wk = 2,808 hrs % hrs setback = unoccupied hours / total heating hours = 2,808/4,368 = = 64.3% So, Fuel saved = annual fuel used x % hrs setback (unoccupied) x % temp setback = = 120,000 gal x x = 10,262 gals or 8.5% of annual heating fuel. At $3.50 per gallon, 10,262 gal x $3.50/gal = $35,918 saved.

42 Energy Calculations: Lower Operating Temperature 42 Windows are commonly opened in your building during winter, due to over-heating. You take temperature readings over several weeks and find rooms ranging from 78 degrees to 84 degrees (average 81 degrees). You determine to improve your room temperatures by re-setting, adjusting and calibrating your controls, with a target of 74 degree average. You use 56,000 therms of gas annually. For space heat only? Trick question? How much gas would you expect to save per year by changing the average room temperatures from 81 to 74 (and no other changes to your systems)?

43 Energy Calculations: Lower Operating Temperature How much gas would you expect to save per year by changing the average room temperatures from 81 to 74 (and no other changes to your systems)? Similar to the night time setback calculation, % temperature decrease = (T old T new ) / T old = (81 74) / 81 = = 8.6% Therefore, 56,000 therms /yr x (0.086) = 4,840 therms saved per year (Note: always use decimal equivalent for the percentage when multiplying) So at a cost of $3.00 per therm, the annual savings is 4,840 therms x $3.00/ therm = $14,519 per year. Again, without spending any money. It is important to remember to apply the % temp savings only to the energy used for heating the rooms. If the building uses gas for other purposes, that energy would need to be subtracted from the total therms used in the calculation. 43

44 44 Energy Calculations: Shutting Down Zones Let s say we have a building with a gymnasium in use four (4) hours every Saturday while the rest of the building was not in use. The gymnasium is in a heating zone that represents 20% of the total building space. The building is normally occupied Monday through Friday from 7 am to 7 pm with a night setback in place after all occupants leave but the entire building is on Saturday when the gymnasium is in use. Assume that the building was heated 7 months from October through April and that the annual heating load was 70,000 therms. How much would the heating cost decrease by only heating the gymnasium area of the building on Saturday?

45 45 Energy Calculations: Shutting Down Zones This Saturday use adds 4 operating hours ( 7pm to 11pm) per week. As stated, the heating season runs from October to April or Number of weeks = 7/12 x 52 = 30 weeks Heating hrs. per year = 30 wks x 12 hrs/day x 5 days/wks = 1800 hrs. plus Saturday hours = 4 x 30 = 120 hours Total heating hrs = = 1920 hrs. Average hourly heating load = 70,000 therms/1920hrs = therms Shutting down 80% of the building for the 120 Saturday hours Therms saved = 0.80 x therms/hr x 120 hrs = 3500 therms, Or, 3,500/70,000 = 5% of the heating requirements At $3.00 per therm, this represents a savings of $10,500.

46 Energy Calculations: Reduced Operating Hours 46 Optimized start-up/shut-down reduces the number of heating plant operating hours by an average of 1.5 hours per day. What is the annual cost savings at $3.50/ gallon of fuel oil. Assume 100 heating-days per year. Each of two boilers has a rated firing rate of 35 gph of oil. Assume that during heat-up the burner is at 100% firing rate and that both boilers are operating. Energy Saved = Gallons/hour x Reduction of Hours of Use At $3.50 per gallon; = 2 x 35 gph x 1.5 hr/day x 100 day/yr = 10,500 gallons saved per year Annual cost savings = 10,500 gallons x $3.50/gallon = $36,750

47 Energy Calculations: Better Operating Hours Match Let s say the you observe that the boiler operation hours mismatched to your building s operating hours. Perhaps the boiler is started up and shut down daily at the same time regardless of building schedule or outside conditions. A test was run to determine the warm-up time of building at different outside temperatures and found that an optimized schedule will reduce boiler run time by 10%. Remember the estimated savings only applies to heating fuel oil: if you have other uses for fuel oil you will need to subtract this usage from your building s total annual fuel usage. So you have tracked the fuel oil usage for heating every month and find 100,00 gallons of No.2 fuel oil are used per year at a cost of $3.50 per gallon. 47 So we an calculate the savings from optimizing the boiler operating hours as Fuel savings = 100,000 gallons x 10% = 100,000 x 0.10 = 10,000 gallons At $3.50 per gallon, 10,000 gallons x $3.50 = $35,000 saved per year.

48 Energy Calculations: Reduced Boiler Cycling 48 Most buildings have more than one boiler or furnace as its heating plant to provide redundancy, assuring some heating will always be available. Typically, buildings with 2 boilers installed, each will be sized at 75% of design load so the total installed heating capacity = 150% (2 x 75) of design load. This is 50% more capacity than will ever be needed! In buildings with 3 boilers installed, each may sized at 50% of design load, the total installed heating capacity again = 150% (3 x 50) of design load. Having more boilers or furnaces installed permits each boiler to be sized at a smaller capacity and still provide for redundancy. But the design day load rarely occurs, maybe only a few hours each year, so most of the year these boilers operate at a part load. As can be seen in the next slide, the boiler efficiency drops dramatically if the on-time is less than 30%.

49 Energy Calculations: Reducing Boiler Cycling 49 Boiler Part-Load Curves Burner Fractional On Time plotted against boiler efficiency Steep fall-off at 30% of Burner On Time Avoid operating boiler with less than 30% on time. Avoid shore cycling. Source: Brookhaven Nat l Lab 1978

50 Energy Calculations: Reduced Boiler Cycling 50 On the design day (10 o F outside temp.) the building already has more heating capacity installed than will be needed. Since, typically, the average winter temperature in NYC is 40 o F. Whenever a boiler capacity is greater than the required load, it will cycle on and off to meet the load requirements. Fraction of design load = Actual load / Design load = (70 o F - 40 o F) / (70 o F - 10 o F) = 30 / 60 = 1/2 = 0.5 If we have 3 boilers installed, each rated for 50% of the design load, the available installed capacity becomes 300% of capacity (150%/0.5) and will operate only 1/3 of the time! When outdoor temp is warmer than the design day, the demand for heat is lower and the boilers are now more Over-Sized and will cycle on and off more frequently.

51 51 Energy Calculations: Reduced Boiler Cycling Assuming a boiler has a rated full load fuel consumption of 20 gal/hr, the resulting savings making modifications to reduce operations from 5 cycles/hr to 2 cycles/hr reduces the percentage of energy loss due to cycling from 8% to 2%, or ( ) / 0.98 = or 6.1% If the boiler operates for 3,000 hours per year and fuel costs $3.50 per gallon 20 gal/hr x 3,000 hrs x = 3,660 gals Cost savings = 3,660 gallons x $3.50/gal = $12,810

52 Energy Calculations: Check Results against bills 52 ENERGY USE RECORD Oil, gal $-Oil Gas,therms $-Gas kwh kw $-Electricity Total $ Annual Totals 121,800 $ 426,300 26,700 80,100 4,670, $ 1,131,400 $ 1,637,800 Energy Efficiency Measure Bathroom Upgrade 25,872 $ 5,174 $ 5,174 Reduce Oil Boiler Hours 10,500 $ 36,750 $ 36,750 Reduce Oil Boiler Cycling 3,660 $ 12,810 $ 12,810 Night Set Back 10,262 $ 35,917 $ 35,917 Boiler Improvement 1,075 3,225 $ 3,225 Lower Operating Temp 4,840 14,520 $ 14,520 Optimized Boiler Operating Hours 10,000 $ 35,000 Zone Shut Down 3,500 10,500 $ 10,500 Measure Totals 34, ,477 9,415 28,245 25,872 5,174 $ 118,896 Percent of Annual Total 28% 28% 35% 35% 1% 0% 7% Comparing the Efficiency Measure savings calculated within this module to the annual energy use record, we can see the reasonableness of the savings estimated. For example, the bathroom lighting upgrade save 1% of the total kwh which seems reasonable for a measure affecting 20 rooms. The oil and gas measures show much higher savings, which could be reasonable but worth double-checking assumptions and calculations. If the savings % had gone much say to 60% - we would have to really look hard to be convinced that the calculated projection is correct.

53 53 Class Review & Reading Assignment O&M in lighting and HVAC can create significant building energy savings. With little or no cost, re-tuning combined with Green Control Strategies can significantly cut building energy needs O&M with a focus on achieving energy savings, strategies to achieve energy reduction in systems: Lighting, HVAC, Boilers, Heating, Cooling How to calculate energy savings? Understand how energy is used by building systems and equipment, and use spreadsheets to calculate cost savings for improvements Decide between two or more alternative projects choices Estimate post-retrofit energy budgets, relate calculations to energy use histories Reading Assignment for Class 18: Herzog, Ch. 6, 7& 8 (finish); Herzog Appendix A (rest) and B