Saving Energy in Existing Multifamily Buildings
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This document summarizes strategies for improving energy efficiency in existing multifamily buildings. It discusses the Center for Energy and Environment (CEE), which conducts research on energy use in multifamily buildings. Key opportunities for energy savings include optimizing existing condensing boilers through proper controls and piping configuration, modifying building ventilation systems to reduce excessive airflow, and installing demand-based hot water recirculation controls. Ensuring success requires focusing on strategies with good paybacks and marketability to building owners.
Saving Energy in Existing Multifamily Buildings
- 1. Saving Energy in Existing Multifamily Buildings Duluth Energy Design Conference February, 2015 Corrie Bastian Center for Energy and Environment
- 2. Pg. 2 Topics • Who is CEE • Energy use in multifamily buildings • Perspective: Understanding the industry • Retrofit highlights • Energy impact • Marketability • Ensuring success: I, O & M best practices
- 3. Pg. 3 Who is CEE The Center for Energy and Environment (CEE) is a nonprofit organization that promotes energy efficiency to strengthen the economy while improving the environment We conduct research and develop programs so that: • Businesses operate more efficiently and profitably; • Government agencies and nonprofits spend less on facilities and functions; • Utilities achieve their energy-efficiency goals at least-cost; and • Households save money and improve comfort.
- 4. Pg. 4 What we do • Energy Program Design and Delivery • Engineering Services • Innovation Exchange • Research • Education and Outreach • Sound Insulation Program • Public Policy • Lending Center
- 5. Pg. 5 CEE multifamily experience • Facility assessments of over 2,000 buildings in Minnesota • Completed over 20 research projects
- 6. Pg. 6 Current multifamily research projects • Condensing boiler optimization • Multifamily ventilation optimization • Demand Controller recirculation loop controls • Multifamily aerosol envelope air sealing • Indoor pool optimization All funded through the MN Department of Commerce’s Conservation Applied Research and Development grant program. The Conservation Applied Research and Development (CARD) grant program is funded by MN ratepayers, and administered by the Minnesota Department of Commerce, Division of Energy Resources
- 7. Pg. 7 Current multifamily energy efficiency programs • Energy Star multifamily 3rd party verifier • One Stop Efficiency Shop lighting program with Xcel Energy • Multifamily Energy Savings program with MN Energy Resources
- 9. Pg. 9 What we know about multifamily buildings “Multifamily buildings are a tough energy efficiency nut to crack” Why? • “Split incentive” / diverging interests between resident and owner • “Lots of players in the orchestra” • Perception that technical challenges outweigh financial benefits
- 10. Pg. 10 Market research on multifamily building owners and managers reveals perceptions of energy efficiency • “Expensive” • “Complex maintenance and upkeep” • “Realized savings are questionable” • “Improved comfort is a big benefit” • “Has to be durable” • “Trustworthy energy efficiency advice is needed”
- 11. Pg. 11 Decision making: Who is who
- 12. Pg. 12 MN multifamily buildings are SOURCE: Minnesota Multifamily Rental Characterization Study, Energy Center of Wisconsin and Franklin Energy, 2013; sampled 120 bldgs in MN (78 in Twin Cities, 66 Greater MN) • 78% “Post-War” and newer stock • Natural gas = common heating fuel (~66%) • Central hydronic = common heat system (83%) 4-6 BTU/ft2/HDD Relatively “young and fit” buildings
- 13. Pg. 13 …And yet outliers in (almost) every category SOURCE: Minnesota Multifamily Rental Characterization Study, Energy Center of Wisconsin and Franklin Energy, 2013; sampled 120 bldgs in MN (78 in Twin Cities, 66 Greater MN)
- 14. Pg. 14 Water and space heating costs dominate SOURCE: Minnesota Multifamily Rental Characterization Study, Energy Center of Wisconsin and Franklin Energy, 2013; sampled 120 bldgs in MN (78 in Twin Cities, 66 Greater MN) = 40% = 15% = 10% = 34% Average Multifamily Utility Costs (per unit / year)
- 15. Pg. 15 …And yet they are a small piece of the expense pie Payroll & Benefits 19% Insurance 4% Taxes 17% Mgmnt Fee 8% Admin 4% Water & Sewer 5% Elec. 3% Gas 4% Trash, Cable, Misc. 4% Repairs 27% Marketing 2% Other 3% Utilities = 12% Source: 2013 MN Multi Housing Association Expense survey. 388 multifamily properties surveyed Average MN Multifamily operating expenses
- 16. A good investment… Has aggressive energy paybacks Lowers O & M costs Improves building comfort Makes things easier for staff Is “tried and true” Is easy to implement Makes everyone look smart i.e. Energy efficiency marketability goes well beyond payback
- 17. MARKETABLE ENERGY EFFICIENCY STRATEGIES FOR MN MULTIFAMILY
- 18. Pg. 18 Good opportunities for energy savings – beyond “the laundry list” • Optimizing existing condensing boilers • Building ventilation modifications • Demand-based hot water recirculation loop controls • Aerosol envelope air sealing
- 19. Pg. 19 Acknowledgements Projects discussed are supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources through a Conservation Applied Research and Development (CARD) program
- 21. Pg. 21 Achieving rated efficiency (>90% efficiency) CONDENSING TEMPS Return water temperature
- 25. Benefits • 4-10% of gained efficiency • Eliminate short-cycling • Getting what you paid “extra” for
- 26. The key: driving down return water temperature • Maximize heat transfer at heating elements • Send lower temp water out to the building • Make sure boiler output matches demand • Make sure your piping isn’t dumping supply water into return • Make sure domestic hot water is not integrated with space heating boiler
- 27. How? • Considerations for an existing condensing system • Proper excess air levels • Adjusting outdoor reset and sequencing/staging controls • Reducing maximum output temp • VFD pumping for increased heat transfer • OR Considerations at time of replacement • Boiler room piping • Choosing a boiler with good on board reset and sequencing/staging controls
- 28. Pg. 28 Excess air can dictate boiler efficiency Image source: industrialheating.com ADJUSTMENTRANGE Measured as % Oxygen in flue gas
- 29. Pg. 29 Condensing boiler sensitivity to excess air • Controlling excess air very important • Excess air reduces concentration of water vapor • Dewpoint decreases Low Excess Air High Excess Air
- 30. Pg. 30 Oxygen levels in flue gas
- 31. Heating elements: You’re stuck with them • It isn’t cost effective to add more • Dirty or blocked radiation affects heat transfer
- 32. Control boilers for lowest possible output • Optimized outdoor reset • Finding the lowest max output temp for the building • Sequencing and staging for optimal efficiency
- 33. Pg. 33 Control the boiler so it doesn’t exceed demand 20F in March
- 34. Pg. 34 Outdoor reset lowers boiler water temperature As outdoor temps get warmer, the building heating load gets smaller and the boiler water temperature can be lowered. -20°F 0°F 20°F 40°F 60°F 80°F 100°F 120°F 140°F 160°F 180°F Boiler water temperature with outdoor reset Space 75F Boiler water temperature, no control
- 35. Optimizing outdoor reset Min OAT for condensing moved from 34F to 22 F Can you go lower? Boilerwatertemp Outdoor temp Adjusted supply curve Adjusted return curve
- 36. Outdoor reset adjustment 14 unit building: 9.5% space heating savings (no cost) Reduced building over-heating
- 37. At replacement: Identify boiler control limitations • This boiler control’s non-adjustable minimum outside temp of 0F is not ideal for MN
- 38. Boiler sequence and firing stage controls: matching output to load for best efficiency Lower output firing stages have increased thermal efficiency Image source: Lochinvar.com
- 39. Lochinvar Knight boiler cascade strategies: Image source: lochinvar.com
- 40. Sequencing boilers: mixed efficiency 41 unit building: 11% space heating savings 3 year payback Reduced short-cycling
- 41. Sequencing/staging: All firing on at once because they can’t talk to each other 32 unit building: 6% space heating savings 5 year payback Reduced short-cycling
- 42. Variable speed pumps (VFDs, VSDs) • Reduce the pump flow during part-load (when zones close) • Allows for lowered return water temperature—more potential boiler condensing conditions • Electricity savings
- 43. Little difference between boiler supply and return temperatures indicates potential for improvement 1- Adjust reset temps as low as possible 2- VFD pump control optimizes heat transfer as zones open and close
- 44. Boiler room piping: address at replacement 1 2 3 4 RETURNBuilding loop Not ideal: Adjacent boilers warm return water
- 45. Better piping 1 2 3 4 RETURNBuilding loop
- 46. Pg. 46 Domestic hot water can dictate return water temps • Traditional coil-in tank requires high boiler temperatures, limiting boiler efficiency during DHW call • Direct-fired condensing water heaters will be more efficient 130°F Boiler 180°F Water heater
- 47. Pg. 47 Summary: getting condensing boilers to condense! • Proper oxygen levels in flue gas contribute to optimal condensing conditions • Maintaining aggressive control settings prolongs condensing capabilities • VFD pump controls reduce pump speeds at part loads to optimize heat transfer • Boiler room piping can dictate return water temps • Choosing direct-fired condensing water heaters over indirect (sidearm) water heaters will maximize efficiency
- 49. Pg. 49 Optimizing ventilation systems ISSUES • High fan power use • Excessive ventilation airflow • Occupant complaints of drafts, odors • Duct leakage • Clogging and other flow balancing problems • Difficult/costly to measure and quantify energy savings associated with retrofitting
- 50. Pg. 50 Central ventilation systems Central apartment exhaust Central corridor/make up air systems
- 51. Pg. 51 Ventilation Improvements – corridor systems • Reduce fan speed to provide code required ventilation flow ISSUES • Design flow rates were much higher than current required flow • Faulty controls/sensors • Flow rates not verified
- 52. Pg. 52 Corridor ventilation retrofit in Minneapolis Project: Re-sheave fan for lower flow • 4,700cfm reduced • 9,611 therms saved • 7,244 kWh saved • $6,899 total savings • <6 month payback
- 53. Pg. 53 Ventilation Improvements – central apartment exhaust systems • Reduce & balance flow • Seal inlets, curbs & ducts • Install high efficiency fans ISSUES • Design flow rates were much higher than current required flow • Unbalanced flow • Flows difficult to verify and seldom measured
- 54. Pg. 54 Central exhaust retrofit in Minneapolis Project: 1- Replace operable balancing louvers with fixed orifices 2- Replace belt drive exhaust fans with high-efficiency type • 2,299 cfm reduced • 4,706 therms saved • 21,979 kWh saved • $5,037 total savings • 7 year payback • Reduced odors and noise
- 55. Pg. 55 Installing fixed balancing orifices Replace balancing devices prone to clogging or tampering Seal duct leakage at inlet Install fixed orifice sized for correct flow, sealed to ceiling
- 56. Pg. 56 Replacing exhaust fans 1. Seal leakage below fans at curb 2. Replace with EC fans with adjustable speed controls 3. Verify flow is correct
- 57. Pg. 57 Trash chutes can affect ventilation performance • Trash rooms may exhaust too much air • Lack of air sealing can cause odor transfer • Ventilation flow may be increased to compensate
- 58. Pg. 58 Addressing the trash chute • Keep trash room doors closed • Seal trash room off from rest of building • If no door, seal chute to compactor/trash bin • Reduce trash room exhaust fan flow rate • Reduce chute cap opening $1,500 savings annually from reduced stack flow
- 59. Pg. 59 Stay tuned • Ventilation assessment manual this spring • Guide for assessment and retrofitting central supply and exhaust systems (and trash chutes) • Audience: HVAC contractors and energy consultants • Project report this summer • Energy savings opportunities found in 18 buildings • Retrofit outcomes on 6 buildings
- 60. Controlling hot water recirculation loops
- 61. Hot water recirculation loops Image source: HMG, Inc
- 62. DHW energy losses Image source: HMG, Inc. Multifamily Central Domestic Hot Water Distribution systems. 2013
- 63. Pg. 63 Enovative’s Demand Controller • Control stops pump when there is no building demand or the recirculation loop temp is above 100F • Pump run time reduced from 24/7 to average 14 mins / day (ARIES Collaborative/Building America study in 2014)
- 64. Pg. 64 Variables that affect savings • Proper Installation • Insulation on recirc loop pipes • Seasonal consumption • Incoming cold water temp • Building consumption habits • “Crossover” DHW Savings Range: 5-15% Average: 9%
- 65. Pg. 65 Rochester installation • 3-story • 39 unit building • Built in 1955 • Failed water heaters • Shower heads and faucet aerators installed along with building assessment 10% DHW savings from Demand Controller Payback = 4 years 540 therms saved, 14 therms / unit
- 66. Aerosol envelope air sealing Concept: • Pressurize apartment unit • Spray air sealing fog • Sealant particles build up on gaps as they exit the envelope
- 67. Pg. 67 Multifamily compartmentalization Creating an interior air barrier around each unit • Reduced stack effect • Reduced noise transfer • Reduced odor transfer/improved IAQ • Increased comfort • Increased energy efficiency
- 68. Pg. 68 Nuts and bolts PREP WORK • Horizontal surfaces covered • Windows, exterior doors covered • Finished floor covered (ideal before flooring is installed) • Door handles covered • Plumbing fixtures covered • Ceiling fans covered • Radiators covered • Sprinkler head openings covered • Remove outlet/switch plates
- 69. Pg. 69 Nuts and bolts SET UP/SEAL • Blower door and nozzles • 100Pa pressurization • ~ 90% RH maintained CLEAN UP • Open windows, purge • Remove masking
- 70. Pg. 70 Preliminary results • Air tightness result: 114 to 25 CFM50 total unit leakage (8 units sealed) • Averaged 0.45 ACH50 • 78% to 95% tighter than the new code requirement of 3.0 ACH50 • 12-13 times tighter than Energy Star requirement for multifamily
- 71. Pg. 71 Leakage reduced over injection period
- 74. Pg. 74 Identifying the opportunity IDEAL CANDIDATES • Moderate rehabs “floors and cabinets” • New construction NOT IDEAL • Where carpet is installed • If occupied
- 75. Pg. 75 Air sealing at lower cost? Aerosol • Prep • Sealing process • Simultaneous air leakage testing ensures results Manual air sealing i.e. caulking/foaming • Architectural specification • Labor • Air leakage test => Uncertain results Vs.
- 76. Pg. 76 Marketable? BENEFITS • Reduced mid and high range noise transfer • Reduced odor transfer • Improved comfort • Simultaneous air leakage testing ensures results • Expedited process, labor savings potential CONSIDERATONS • Cost • Not a solution for large air leak gaps • Rehab or new construction only • Balanced ventilation is crucial
- 77. Pg. 77 Stay tuned for more info (Jan 2016) Study will look at : • 6 test sites; Rehabs and new construction in MN • Enabling commercialization of process • Air leakage reductions • Sound attenuation • ID leak site locations with fluorescent dye/black light photography • Evaluation of time and materials required
- 78. Pg. 78 More info CEE programs and research: mncee.org
Editor's Notes
- #4: The Center for Energy and Environment (CEE) is a nonprofit organization that promotes energy efficiency to strengthen the economy while improving the environment We conduct research and develop programs so that: Businesses operate more efficiently and profitably; Government agencies and nonprofits spend less on facilities and functions; Utilities achieve their energy-efficiency goals at least-cost; and Households save money and improve comfort.
- #5: CELast year was CEE’s 35 anniversary. Since beginning, working in energy efficiency research, Focused on practical and cost-effective energy solutions that really work—Are field tested in real buildings Our research informs our programs
- #6: CEE has been involved in MF since early 1980s Started w research on boiler controls and identification of other opportunities (study published 1984) Ran programs in MN, also involved for a while with Focus on Energy.
- #7: We are involved in CARD grant research funded through the Division of Energy Resources. We’re also involved with a benchmarking pilot, through a company called EnergyScoreCards. We have about 500 MF bldgs throughout the state enrolled in this. The idea is we’ll see if providing MF building owners and managers with a benchmark of their energy usage, compared to similar buildings, will provide energy savings in itself, sort of like an OPOWER for MF buildings.
- #9: Now I’ll talk about some characteristics of MF sector relevant to energy use.
- #10: Resident may pay bills, but have no influence over energy efficiency in building, or owner may pay bills but resident has no incentive to save or conserve.
- #12: Owner decision making dominates small buildings, as buildings get larger—more variety of staff can be involved. Other staff make decisions, with approval from upper management.
- #13: Natural gas = relatively low cost heating fuel (compared to electric, fuel oil) Hydronic heat = less energy savings potential compared to steam, but easier to work compared to indiv forced air Post war buildings = tighter envelope (masonry buildings), more efficient heat (hydronic) FYI, unit size 1,000ft2
- #15: A study came out last year based on 120 multifamily buildings in MN. Here is the average gas and electric usage for MN multifamily buildings, expressed on a per unit, or per apartment, basis. This is for centrally heated gas buildings, where the owner pays the entire gas bill (most common in MN) And resident pays own electricity, including A/C (window units) MORE DETAILS: Only 13% of units are individually metered for gas (of those with gas heat). Only 4% of units are NOT individually metered for electric. Lighting is 990 kWh of total or about 22% of total. Cooling is 530 kWh of total, or about 11% of total. **Based on 9 cents/kWh for master-metered accounts; 11 cents/kWh for individually metered accounts. **Based on 62 cents/therm for master-meterd accounts; 78 cents/therm for individually metered accounts
- #16: Utility expenses are not 1st 2nd or 3rd priority for spending, but more like the 7th or 9th When I get excited that I can save them 15% on their utilities—maybe $5,000—it’s important for me to remember that this is within a larger expense pool of 275,000. Your efficiency improvement will save 1.25% of overall expenses.
- #18: Now I’ll talk about some characteristics of MF sector relevant to energy use.
- #20: We would like to acknowledge and thank the MN Division of Energy Resources and the Conservation Applied Research & Development (CARD) support that funded this research.
- #22: Condensing boilers are more efficient—but how much more depends on how often they are able to “condense”
- #29: RUSS provided code min o2 levels: CO less than 0.04% “air free” 400ppm O2 induced draft: 4%-10%, power burner: 3-10%
- #31: Code allowance of oxygen levels—Russ will check and get back to me (max CO allowed) Tune valve to min oxygen, while keeping below max co Eff readout from comb analysis tool will never read above 90—does not factor in condensation
- #33: Sequencing and staging: running boilers at low output—show manufacturer’s curves for eff at lower input rate. Watch out for: short-cycling. Levels of control and control interaction.
- #35: Great for any boiler—can go further with condensing boilers
- #41: Single stage combined with 2 stage controller—2 boilers fired (condensing and non condensing). = shorter firing intervals, more efficient Solution: 3 stage control, no rotating lead
- #42: Excessive BTU output -may exceed building demand—return water will come in hotter -shorter firing intervals (short-cycling)
- #47: Better efficiency from sep direct fired condensing system. Sidearms require 180F boiler temps for hx
- #48: Piping in series—include diagram Straining cleaning before install??
- #51: Out of whack buildings. Higher flows up top. Near zero flows near bottom. Balancing flows and reducing overall flows balances and delivers the appropriate amount of ventilation without over-ventilating.
- #62: Purpose is to deliver hot water quickly to far reaches of building
- #64: Used in 100s of buildings in NY, CA, IS
- #66: 1st install in MN When bundled with utility provided showerheads and aerators, payback 1.8 yrs No residents noticed any change
- #67: Concept: A recently developed technology at UC Davis for -automating the envelope sealing process -process involves briefly pressurizing a building to normal testing pressures while applying an aerosol “fog” to the building interior. -As the air escapes through leaks in the exterior shell of the building (including leaks between apartments), the aerosolized sealant is transported to the leaks, and seals them as it tries to escape. -Existing blower door equipment is used to facilitate the sealing process as well as to provide real-time feedback and a permanent record of the sealing that is occurring. -This technology is thus capable of simultaneously measuring, locating, and sealing leaks in a building envelope (using aerosol particles has been successfully tested in the laboratory and demonstrated in full-scale applications. The aerosol envelope sealing e providing permanent documentation of the sealing process.)
- #69: 2 near term applications: new construciton, post drywall/tape. Rehabs : at time of carpet/cabinets Seal windows? Dave will confirm Gaps filled with fiberglass seal? Tried that. Yes, it appears that will work. Any gap 3/8” or narrower. Duct board in aeroseal process of sealing ducts and it works on duct board. Dave will email uc davis guy. Mark Modera at UC Davis developed this technology. Remain sticky/stain over time? A lot of durability testing on duct sealant. Little degradation over time. This sealant has been used for other applications (tremco is manufacturer). Lots of prep work Cover all horizontal surfaces nozzles should be placed, at a minimum, in every bedroom and living area of the apartment nozzles generate a spray jet that travels about 8 feet Cleanable from surfaces
- #70: How is RH maintained? Airflow is monitored and RH of incoming air and heat provided—to determine how much liquid should be injected. At commercialization—this will be automated. Nozzle pressure 60 psi and 90 psi and liquid flow rates between 20 ml/min and 50 ml/min Heating the air in the dwelling will increase the water carrying capacity of the air which allows for higher sealant injection rates and reduced sealing times. Equipment: modified blowerdoor panel, with 2 holes for duct blaster and opening for cables (injection lines, power cords, etc) ductblaster on outside, connected to heater on inside. Protects duct blaster from getting sealant on it. UC davis is looking for manufacturer to commercialize this.
- #71: The sealant worked very well, sealing the units 78% to 95% tighter than new code requirement of 3.0 ACH50. Blower door fan was measuring between 25 cfm to 114 cfm at 50 pascals after sealing. Approx 1,000ft2 apts Before air-sealing tightness: 2.0-2.9 ACH50 (433 CFM50)
- #72: How do you know when to stop? Monitor rate of sealing—looking into this to optimize the cost / benefit. What’s the goal? If energy savings, then stop earlier. If goal is reducing sound transmission, or air transfer, then go longer. Most took 2 hours, ones that went longer had some issues with heater, equipment.
- #75: Does code require air tightness tests on multis? No…mpls has sound transmission testing requirement though. Fredrichs has had experience where air sealing helps to pass sound transmission requirement. Meeting higher energy performance standards energy star, LEED? Can seal unit by unit, with adjacent unit occupied. Pressurized adjacent unit? Or address major leaks between units before hand. (this wasn’t a big issue during the first test—not much went into adjacent units)
- #76: Eliminate need for fire caulking penetrations at wall cavities ? Would not eliminate leakage that happens after the sealing (cabinets install, tstat/lighting installs, etc.) 2 parts to the prep: day of—sealing and covering. And days before—work coordination and inspect for readiness. Did 2/day on the first 4-5 hours each NEED FOR BALANCED MECHANICAL VENTILATION! If design previously included bringing in air from outside, than that will need changing: trickle ventilation or balanced ventilation. Not supply only or exhaust only.
- #77: How does material age? Toxicity? “low ingestion hazard” Main issue: person who works with it day-to-day. Rubber gloves and respirator when airing out unit.
- #78: When will study wrap up? Testing 3 new construction buildings, and 3 rehab sites. End of year final report (end of 2015). How many total sites? 6ish Still looking for sites in/near metro area. UC Davis and contractor on east coast awarded contract for moderately sized military buildings
- #80: Applications for the program up front