Energy-Efficient Controls for Multifamily Domestic Hot Water · Advanced Residential Integrated...
Transcript of Energy-Efficient Controls for Multifamily Domestic Hot Water · Advanced Residential Integrated...
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Advanced Residential Integrated Energy Solutions
Building America Webinar: Central Multifamily Water Heating Systems
January 21, 2015
Energy-Efficient Controls for Multifamily Domestic Hot Water
Jordan Dentz and Eric Ansanelli The Levy Partnership, Inc.
New York, NY
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Research Sponsors
• The ARIES Collaborative is a Department of Energy, Building America research team led by The Levy Partnership.
• ARIES focuses on reducing energy use in new and existing residential buildings
• Research conducted by:
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Introduction Approach Results Conclusion
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Water Heating is one of the largest multifamily energy uses.
Energy Consumption
Heating 43%
DHW 19%
Cooling 6%
Refrigerators 6%
Other 26%
Average Site Energy End Use for Multifamily (5+ Units) Buildings
Source: U.S. Energy Information Administration, 2009 Residential Energy Consumption Survey
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Typical DHW energy distribution with continuous pump operation
Values based on NYSERDA Site #2
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Context
• Recirculating domestic hot water (DHW) systems are common in commercial and multifamily buildings
• Recirculation pumps often run 24x7 - increasing energy consumption because the pipes radiate heat continuously, even during periods when there is no demand for hot water.
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What is a DHW recirculation system?
Recirculation piping continually moves hot water from the point at which it is heated to the fixtures throughout the building, minimizing wait time.
Figures: HMG, Inc. (left), Danfoss (right)
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Why a Recirculation Pump Is Needed
• A recirculation pump keeps the DHW piping loop hot as it gradually loses heat to the surrounding air, reducing wait time at the faucets.
• Without a recirculation pump, one
has to wait for the cooled, stagnant water to be removed from the loop.
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Types of DHW Control
• Timer Control • Temperature Control • Temperature Modulation Control • Demand Recirculation Control • Demand + Temperature Modulation Control
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Timer Control
• Turns pump on and off according to a time schedule
• Time schedule off periods should approximate the peak DHW usage periods at the building.
• When a user demands hot water during an "off" period, they will waste water as they wait for the temperature to increase.
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Temperature Control
• Automatically turns pump on and off based on temperature (usually 120˚F) via a sensor on the return line.
• Less pump electricity, but keeps the distribution loop hot to maintain 120˚F even when there is no demand.
• Often turned up past the supply temperature by building staff (effectively bypassing the control).
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Temperature Modulation Control
• Modulates DHW supply temperature according to a daily schedule.
• Lowers supply water temperature during periods of low demand – late night and mid-day in residential buildings.
• Energy savings can be achieved via lower distribution losses, but pump runs continuously.
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Demand Control
• Uses two pieces of information 1. Real-time user demand (detects
flow) 2. Return water temperature (pump
cuts in below 100˚F).
• The pump only runs if both conditions above are satisfied or the pump has not run for five hours
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Introduction Approach Results Conclusion
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Key Questions
1. How do control strategies compare to constant pumping and to each other in terms of energy savings?
2. What is the cost effectiveness of a multifamily DHW control system retrofit?
3. How might the interactive effects between DHW energy savings and the heating/cooling loads affect payback?
4. What potential complications might be encountered in getting these controls to work well?
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Previous Research
Report Location Building Characteristics Control Type Annual Savings
Benningfield (2009) California 35 sites, 1,540 units Demand 35 therms/unit
Enovative (2008) Los Angeles, CA 5 story, 50 units Demand 30%
Enovative (2009) Los Angeles, CA 5 story, 189 units Demand 12%
Enovative (2010a) Escondido, CA 2 story, 8 units Demand 18%
Enovative (2010b) Irvine, CA 3 story, 21 units Demand 16%
Enovative (2011) Malibu, CA 30 units Demand 15%
Goldner (1999) New York City 6 sites, 5-6 stories, 25-103 units
Timer (nighttime off) 6%
Timer (peak hours off) 6%
Return temperature 11%
HMG (2008)
Saint Helena, CA 2 story, 8 units
Demand 44%
Temperature modulation 35%
Timer (late evening off) 1%
Oakland, CA 3 story, 121 units
Demand 5%
Return temperature -5%
Timer (late evening off) -1%
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Building Characteristics
Property Building A Building B Building C Building D
Collection Period January 2013 - January 2014
January 2013 - January 2014
August 2013 - April 2014
August 2013 - March 2014
Control Methods Tested All All Demand Only All
DHW System Dedicated boiler and storage tank
Winter: tankless coil with mixing valve,
Summer: dedicated
Dedicated boiler and storage tank
Dedicated boiler and storage tank
Number of Bedrooms 66 294 81 72
Number of Floors 7 15 3 3
Average Supply Temperature 135°F 119°F 159°F 131°F
Average DHW Gallons/Bedroom/Day 34 38 38 41
Measured Boiler Efficiency 82% 80% 83% 85%
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Control and Monitoring Equipment
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Test Strategy
• Demand recirculation • Temperature modulation
– 125°F for 4-5 hour morning and 6-7 hour evening “peaks”
– 110°F midday and late night
• Demand with temperature modulation control
• Each strategy alternated for 1-3 weeks in succession with baseline mode through all seasons
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Accounting for Changes in Temperature and DHW Use
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Introduction Approach Results Conclusion
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Installed Costs
• Demand Recirculation Control: $3,000 – without new pump: $2,500
• Temperature Modulation Control:
– storage tank control: $2,000 – new electronic tempering valve:
$5,300
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Supply & Return Temperatures
Property Building A Building B Building C Building D
Baseline 138°F/135°F 125°F/122°F 159°F/153°F 132°F/129°F
Demand Control 139°F/98°F 120°F/83°F 159°F/77°F 131°F/95°F
Temperature Modulation
130°F/128°F 117°F/114°F - 128°F/125°F
Demand Control & Temperature Modulation 130°F/98°F 114°F/79°F - 129°F/97°F
Makeup Water 57°F 53°F 48°F 55°F
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Recirculation Pump Runtimes
• Average of 14 minutes/day
• 99% reduction from continuous operation
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Measured DHW Fuel Savings
Property\Mode Building A Building B Building C Building D
Annual Baseline DHW Consumption 175 therms/br 94 therms/br 184 therms/br 112 therms/br
DHW Fuel Reduction with Demand Control
12% (20.4 therms/br)
9% (8.0 therms/br)
6% (10.3 therms/br)
7% (8.3 therms/br)
DHW Fuel Reduction with Temperature Modulation
2% (3.4 therms/br)
8% (7.8 therms/br) - 2%
(1.9 therms/br)
DHW Fuel Reduction with Demand Control & Temperature Modulation
15% (25.9 therms/br)
12% (11.3 therms/br) - 15%
(16.2 therms/br)
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Space Conditioning Interactivity
For central scenario: • Heat penalty was 37% of
the DHW fuel reduction • Average cooling bonus was
10% of total dollar savings • Reduced pump electricity
contributed 25% to dollar savings
Parameter Least Effect
Middle Case
Greatest Effect
Heating Efficiency 85% 75% 65%
Heating Hours 2,686 3,263 4,074
Cooling Efficiency (Btu/Wh) 8 10 12
Cooling Hours 1,080 540 540
Percent Interaction 50% 75% 100%
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Simple Payback
Property Building A Building B Building C Building D Annual DHW Cost (incl Recirc Pump Electricity) $15,900 $31,200 $16,400 $9,200 Installed Cost of Demand/Temp Mod. Controls
$3,000/$2,000 $2,500/$5,300 $3,000 $3,000/$2,000 Demand Control Payback 2.1 1.0 3.0 3.7 Temperature Modulation Payback 11.2 3.0 - 18.5 Demand Control & Temperature Modulation Payback
3.0 2.5 - 4.0
• Average annual cost savings, including interactive effects:
• 9% with demand controls • 3% with temperature modulation controls • 12% with both combined
• Worst-case average payback: <4 years for demand control; 21 years for temperature modulation
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Introduction Approach Results Conclusion
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Lesson: Demand Profiles
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Lesson: Commissioning
Site A
Site B
Site D
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Boiler Runtime vs. DHW Makeup Water Temperature
1.50
2.00
2.50
3.00
3.50
4.00
12/7/2012 1/26/2013 3/17/2013 5/6/2013 6/25/2013 8/14/2013 10/3/2013
Boi
ler R
untim
e/D
ay
Boiler Runtime/DayNormalized Boiler Runtime/Day
40.0
45.0
50.0
55.0
60.0
65.0
70.0
12/7/2012 1/26/2013 3/17/2013 5/6/2013 6/25/2013 8/14/2013 10/3/2013
Mak
e-up
wat
er
tem
pera
ture
(F)
TC
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Comparison with Prior Studies
• Average 9% and 14% DHW fuel savings from demand and demand + temperature controls, respectively
• Prior studies showed 12-44% DHW fuel savings with demand recirculation
• Prior studies did not account for interactivity
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Mixing Valve Concerns
• Concerns: – Mechanical mixing valves
• Internal bellows mechanism can fail due to thermal stress
• Non-continuous flow can void warranty
– Electronic mixing valves • Potential to send un-tempered
hot water with non-continuous flow
• Doesn’t void warranty…
• Possible Solutions: – Mechanical mixing valves
approved for non-continuous flow
– Dummy recirculation loop
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Electronic Mixing Valve Supply Temperatures
Electronic Mixing Valve: Highest Recorded 5-Minute Average Temperatures
Continuous Flow 145°F
Demand Recirculation 144°F
Temperature Modulation 132°F
Demand + Temp Modulation 147°F
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Storage Tank Overheating Issue?
Continuous recirculation pumping
Demand-controlled recirculation pumping
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Legionella?
• Temperatures of 77 to 108°F can provide favorable conditions for legionella growth
• OSHA discourages demand control; ENERGY STAR recommends it; California building code requires it for new construction
• Research needed to determine the relative risk of bacterial establishment in DHW recirculation loops with frequent exchange of water
Source: Wikipedia
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• All DHW controls implemented without complaints • DHW demand profiles did not show pronounced peaks and
troughs – constant, low supply temperature might be ideal • Costs depend on existing DHW configuration • Demand control paybacks of 1-4 years, also depends on
building size
Conclusion
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Next Step: 40-Building Rollout
• We’re installing demand controls in 40 multifamily buildings and monitoring performance with NYSERDA.
• Buildings in New York welcome to participate
• Exploring optimized supply temperature and electronic mixing valve issues
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Advanced Residential Integrated Energy Solutions
Thank You.
Jordan Dentz Eric Ansanelli
The Levy Partnership, Inc. 1776 Broadway, Suite 2205
New York, NY 10019 [email protected]
(212) 496-0800 Ext 130 [email protected]
(212) 496-0800 Ext 170