DOMESTIC HOT WATER
MECHANICAL SYSTEMS - MULTIFAMILY
Domestic Hot Water
1 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Learning Objectives DOMESTIC HOT WATER
By attending this session, participants will: • Be exposed to the various models of domestic hot water (DHW) heaters. • Learn the importance of water temperature for safety and energy savings. • Understand the pros and cons of recirculating and nonrecirculating systems. • Be introduced to various types of mixing valves. • Learn to measure apartment water usage, including leaks, and how to reduce usage to save energy.
2 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Domestic Hot Water A Big Piece of the Energy Pie DOMESTIC HOT WATER
Energy Usage
3 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Domestic Hot Water Heater Types DOMESTIC HOT WATER
• • • • • •
Stand-alone water heaters Indirect water heaters Boiler and storage water heaters Heat exchangers Tankless coil water heaters Instantaneous water heaters
4 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Stand-alone DHW Heater DOMESTIC HOT WATER
• Separate combustion appliance from the heating system; has its own burner. • Technologies are as varied as they are for boilers: – Atmospheric combustion – Sealed combustion – Natural draft – Forced draft – Condensing – Can also be electric Photo source: Steven Winter Associates 5 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Stand-alone DHW Heater– Natural Draft #1 DOMESTIC HOT WATER
Most common type. • Draft diverter is open to the room. • Poor draft regulation over the fire.
Draft diverter
A burner zone in an atmospheric DHW heater Photos source: Steven Winter Associates 6 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
Typical natural-gas-fired atmospheric water heater eere.energy.gov
Stand-alone DHW Heater– Natural Draft #2 DOMESTIC HOT WATER
Advantages • Cheap. • Cheap. • Cheap. Disadvantages • Very inefficient. • High standby losses when off due to open combustion chamber. • Poor draft control. • Many models have open pilot light. Photo source: Steven Winter Associates 7 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Stand-alone DHW– Forced Draft #1 DOMESTIC HOT WATER
• Have a power burner on bottom or fan-assist on top. • Better control of combustion conditions. • Higher efficiency than atmospheric combustion, natural draft models.
Photo source: Steven Winter Associates 8 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Stand-alone DHW– Forced Draft #2 DOMESTIC HOT WATER
Advantages • More efficient than natural draft models. • Better-controlled draft. • Lower standby losses. • Better insulated. Disadvantages • Higher initial cost. • Not capable of condensing. • Often can’t be retrofit into existing chimneys used for natural draft boilers. Photo source: Steven Winter Associates 9 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Stand-alone DHW– Condensing #1 DOMESTIC HOT WATER
• Very high efficiency. • Takes advantage of low temperature of entering water to create condensing conditions in burner. • Has highly tuned burner. • Highly insulated tank. • Can’t be vented in the same chimney as natural draft equipment.
Photo source: Steven Winter Associates 10 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Stand-alone DHW– Condensing #2 DOMESTIC HOT WATER
Advantages • Most efficient. • Precision combustion. • Lowest standby losses. • Less expensive venting. Disadvantages • Highest initial cost. • More complex venting. • Can’t share venting with natural draft appliances.
Photo source: Steven Winter Associates 11 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Indirect Water Heaters #1 DOMESTIC HOT WATER
• Also called “integrated tank” or “indirect-fired tank.” • Combustion takes place elsewhere. • Heat exchanger coil within uses boiler water to warm tank’s contents. Boiler and tank water never mix. • Water supplied to coil needs to be ~20°F hotter than tank. They’re only as efficient as the boilers that supply them.
Heat exchanger
Indirect water heater Photo source: Heat Transfer Products
12 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Indirect Water Heaters #2 DOMESTIC HOT WATER
• Advantages vs. stand-alone water heaters – With a good boiler, more efficient than stand-alone tanks (except condensing models). – Only one combustion appliance (boiler) – lower maintenance. – Last longer than stand-alone units, stainless steel more durable than glass-lined tank. • Disadvantages – More expensive initially. – Boiler must be kept at a higher temperature (such as 150°F) to create DHW at 130°F. May not promote condensing in condensing boilers. Indirect water heaters Photo source: Steven Winter Associates 13 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Boiler and Storage Tank #1 DOMESTIC HOT WATER
• Similar to indirect-fired tanks, except no heat exchanger. • Common for large buildings. • Better option than most stand-alone tanks. • How do you tell the difference between this and an indirect-fired tank? – 3 pipes instead of 4
Boiler and storage tank Photo source: Steven Winter Associates 14 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Boiler and Storage Tank #2 DOMESTIC HOT WATER
• Advantages – Boiler water can be kept at lower temperature (~130°F), which is adequate for storage tank. – Low maintenance, especially stainless steel tanks. – Single combustion appliance. – Can be efficient with an efficient boiler if piped correctly. • Disadvantages – More expensive initially in heating climates – must have a separate dedicated DHW boiler.
Boiler and storage tank Photo source: Steven Winter Associates 15 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Boiler and Heat Exchanger #1 DOMESTIC HOT WATER
• One of the most efficient water heating methods available for large buildings with condensing boilers. • Water from boiler and fresh water pass through alternating grooved plates – two streams of water never cross. • Very quickly warms the water to close to boiler water temperature (within 1 – 3°F).
A plate and frame heat exchanger
Two views of the metal plates
Photo source: Steven Winter Associates 16 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Boiler and Heat Exchanger #2 DOMESTIC HOT WATER
• Temperature difference between inlet and outlet is small, ~1°F – 3°F. • Boilers can run at a low temperature (132°F supply) to make DHW (130°F) from this system. This can help condensing boilers condense. • Requires a few more pumps. • Very high capacity system – excellent application for larger buildings with condensing boilers and constant recirculation. 17 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Steam-to-DHW Heat Exchanger DOMESTIC HOT WATER
• Similar to boiler heat exchanger. • Present in district steam buildings and some steam boiler systems.
Photos source: Steven Winter Associates
Tube and shell heat exchanger graphic by SEC heat exchangers
18 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Tankless Coil Water Heater #1 DOMESTIC HOT WATER
• Other common names: – Quick coil. – Lindy coil. • Heat exchanger coil. submerged in boiler water. • DHW never contacts boiler water. • Many forms depending on boiler type.
Tankless coil on Scotch marine boiler Photo source: Steven Winter Associates 19 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
Graphic source: www.energysavers.gov eere.energy.gov
Tankless Coil DOMESTIC HOT WATER
Coil mounted on front of Scotch marine boiler
• The coil could be mounted on the side of a cast iron boiler. • A single boiler produces hot water or steam for heat and hot water for potable use. • Boiler water must be kept warm at all times, which is inefficient. Tankless coil on Scotch marine boiler Photo source: Steven Winter Associates 20 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Tankless Coil Water Heater #2 DOMESTIC HOT WATER
• Advantages – No separate combustion appliance needed for DHW.
• Disadvantages – Boiler must be kept on all summer at 160°F or hotter. – Very large and inefficient boilers are often run year-round.
• Not needed for many higher-efficiency boilers (indirectfire, storage, or heat exchanger), which use other methods to heat water. • Only as efficient as the boiler it’s mounted in. • As a replacement, consider recommending a separate stand-alone condensing water heater to handle summer DHW load. 21 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Instantaneous Water Heater #1 DOMESTIC HOT WATER
• Sometimes called “tankless” water heater (not same as tankless coil). • Independent combustion appliance with no storage capacity. • Usually used in single-family homes or individual apartments in multifamily buildings, but can be used for small multifamily. • Provides a continuous flow of hot water that is made on demand. • Gas-fired and electric models available.
Two models of instantaneous water heaters
Photo source: Noritz Water Heaters 22 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Instantaneous Water Heater #2 DOMESTIC HOT WATER
• Advantages – Several highly efficient models available, including condensing. – Provides continuous, “endless” stream of hot water. – For larger multifamily buildings, can be banked for larger capacity. • Disadvantages – Limited capacity requires multiple unit installations for larger buildings, which are more expensive to vent and maintain. May be cheaper to buy a single efficient boiler with larger capacity.
23 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Electric Instantaneous Water Heater DOMESTIC HOT WATER
• Advantages – Requires no separate hot water distribution. – Small units can be installed under sink at point of use. • Disadvantages – Electricity is fairly expensive. – Draw can strain older wiring.
Photo source: Marey Heater Corp 24 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Rating Water Heater Efficiency DOMESTIC HOT WATER
• Common terms: – Energy factor (EF) – Thermal efficiency
The EnergyGuide sticker shows how this model compares to other units in the same class of water heaters.
Photo source: Steven Winter Associates 25 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Energy Factor DOMESTIC HOT WATER
• Total useful energy output divided by total energy input, expressed as a decimal. Indicates how efficient a technology is. • Rating used for smaller-capacity units – generally residential size, but can be used for gas units up to 100 gallons. Limited applicability to multifamily. – EF for inefficient atmospheric water heaters is very low – around 0.50. (Less than 50% of the energy input is actually useable.) – EF for higher-efficiency gas heaters can be in the 0.80s. – EF for electric units can be very high – in the 0.90s – but electricity can be very expensive.
26 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Thermal Efficiency #1 DOMESTIC HOT WATER
• Measure most common to larger water heaters and boilers in multifamily buildings. • Measure of how much energy actually goes into heating the water. • Does not take into account energy lost when heater is off, which can be significant. • For indirect-fired, storage, and heat exchanger heaters, thermal efficiency of the boiler supplying the hot water is what matters.
27 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Thermal Efficiency #2 DOMESTIC HOT WATER
Find the thermal efficiency on the nameplate of this forced draft boiler. Thermal efficiency = output ÷ input (expressed as a percentage) Output ÷ input = 3,415,000 BTUH ÷ 4,287,000 BTUH Thermal efficiency = 79.7%
Photo source: Steven Winter Associates 28 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Thermal Efficiency #3 DOMESTIC HOT WATER
Thermal efficiency does not tell the whole story. • Thermal efficiency does not measure standby loss or cycling losses. • Both of these losses are greater for natural draft than forced draft boilers. What’s the thermal efficiency for this natural draft boiler? Output ÷ input = 680,400 BTUH ÷ 840,000 BTUH Thermal efficiency = 80.9% Photo source: Steven Winter Associates
29 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Water temperatures matter. #1 DOMESTIC HOT WATER
• Making 130°F hot water in a boiler requires one of the following: – Plate-and-frame heat exchanger at 132°F. – Storage tank at 140°F. – Indirect-fired tank at 150°F. – Tankless coil in boiler at 180°F. • Other boilers must be kept hotter to avoid condensation, which they aren’t built to withstand. • With higher temperatures, condensing boilers will not condense all the time.
30 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Water temperatures matter. #2 DOMESTIC HOT WATER
• Temperature monitoring is important. – Too cold – Legionella (less than 115°F) A liquid-filled temperature gauge with large dial, after mixing valve, is important.
– Too hot – Scalding
Temperature of Hot Water
Time to Produce 2nd and 3rd Degree Burns
160°F
About ½ second
150°F
About 1½ seconds
140°F
Less than 5 seconds
130°F
About 30 seconds
120°F
More than 5 minutes Photo source: Steven Winter Associates
31 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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How does water ever get that hot? #1 DOMESTIC HOT WATER
• Old distribution systems often leave people cold. • A long pipe run means long waits for hot water. • Complaints of no hot water or long waits make the building super crank up the temperature on the water heater.
Furthest tenant complains
Graphic source: Steven Winter Associates 32 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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How does water ever get that hot? #2 DOMESTIC HOT WATER
• Uneven temperatures – some are just right and some are too hot. • Much water is wasted getting hot water to the last fixture.
160oF
Burns in about ½ second!
Just hot enough 120°F
Way too hot! 160°F
Photo and Graphic source: Steven Winter Associates 33 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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The False DHW Loop #1 DOMESTIC HOT WATER
Retrofit: Add a bit of piping and a small recirculating pump to make a false loop in the basement. • Reduces wait times. • Saves water. • Saves fuel – heater doesn’t need to produce very hot water. • Safer – water leaving boiler room can be a much lower temperature. Best applied to buildings with 8 or more units.
Graphic source: Steven Winter Associates 34 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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The False DHW Loop #2 DOMESTIC HOT WATER
• The recirculation pump: – Is small (1/40 – 1/16 HP) and uses minimal electricity. – Needs a flow rate of only a few GPM. – Should be a one-piece wet-rotor circulator pump, which is maintenance-free. – Must be made of bronze to protect water quality and to protect the pump from corrosion by constant fresh water.. Photo source: Taco 35 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Whole-building Hot Water Recirculation DOMESTIC HOT WATER
• Common in newer buildings. • Most systems run constantly. • Opportunities to save energy in these systems: – Pumps use electricity. – Recirculating hot water increases heat loss.
Place aquastat here. Control pump by aquastat.
Graphic source: Steven Winter Associates 36 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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DHW Recirculating Pump and Sensor DOMESTIC HOT WATER
• Aquastat senses temperature. • Pump set to turn on when temp dips below 110°F and turn off when temp goes above 115°F. • Pump will only run when temp in loop drops. • Saves electricity and hot water. • Cannot be used with most types of mixing valves. Photo source: Steven Winter Associates 37 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Thermostatic Mixing Valves DOMESTIC HOT WATER
• Sometimes generically called a “Holby valve,” though there are several manufacturers. • Work best with constant recirculation. • Fail in the HOT position = dangerous. • All-metal design. • Adjustment by screw on unit. • Inexact control.
Graphic source: Holby Valves
Photos source: Steven Winter Associates 38 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Electronic Mixing valves DOMESTIC HOT WATER
• Accurate, can use lower temperatures, safer. • Fail in closed (cold) position. • Help reduce scald problems. • Good ones operate across various pressure settings. • Require constant recirculation to work.
Graphic source: Heat-Timer
Photos source: Steven Winter Associates 39 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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DHW Electronic Mixing Valve Retrofit DOMESTIC HOT WATER
Existing thermostatic mixing valve replaced with new electronic mixing valve for finer control and lower temperatures.
Combined with recirculation, allows lower and more consistent water temperatures to be delivered. New temperature sensor and control for valve Photos source: Steven Winter Associates 40 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Water Booster Pumps DOMESTIC HOT WATER
• Many on 24/7, “running blind.” • Excess pressure is handled by bypass in piping; pumps always run at full power. • VFD can help regulate to minimum pressure required. • Motors must be compatible with VFD, insulation class F or H. • Recommend upgrading systems older than 20 years and larger than 7.5 HP. Photo source: Steven Winter Associates 41 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Apartment Water Usage DOMESTIC HOT WATER
• Methods of measurement – Flow bag – Digital thermometer – Pressure gauge
• Quantify leaks (www.awwa.org/awwa/waterwiser/dripcalc.cfm) • One drip/second equals: • 8.6 gallons/day • 259 gallons/month • 3,154 gallons/year
42 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Methods of Measurement #1 DOMESTIC HOT WATER
“Flow bag” flow metering device Use with a stopwatch to determine flow rate. 1. Turn fixture on. 2. Put bag under for exactly 5 seconds. 3. Remove bag and turn off water. 4. Hold bag upright to read flow. Federal maximum flow rates for new aerators: • Kitchen − 2.2 GPM • Bathroom − 2.2 GPM • Shower − 2.5 GPM Faucets with flows greater than these should get new aerators/showerheads.
Photo source: Steven Winter Associates 43 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Methods of Measurement #2 DOMESTIC HOT WATER
Digital temperature gauge • Use throughout the building to diagnose recirculation and temperature problems: – Long wait times for hot water. – Unsatisfactory delivery temperatures. • Temperature at the tap should be no greater than 120°F.
Photo source: Steven Winter Associates 44 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Methods of Measurement #3 DOMESTIC HOT WATER
Check water pressure at top floor: • Used to check on water booster systems. • Water pressure should be about 30-40 psi at highest floor. • If greater, booster pump settings may be reduced. • Most aerators are rated at 60 or 80 psi and decrease pressure proportionally with flow.
Photo source: Steven Winter Associates 45 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Hot Water Use is Different inby Every Building "[CLICK DOMESTIC HOT WATER
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Name of Chair
46 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Aerators DOMESTIC HOT WATER
• Aerators are: – Inexpensive. – Effective. – Subject to tampering. – Relatively short lived (~7 years average). • Tamperproof models are available.
47 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Low-flow Showerhead and Aerators DOMESTIC HOT WATER
• As a rule, recommend low-flow aerators and showerheads with the following flow rates: – Showerheads – 1.5-1.75 GPM – Kitchens – 1.5 GPM – Bathrooms 1.0 GPM
1.0 GPM aerator
Niagara Earth 1.5 GPM showerhead
Photo source: Steven Winter Associates 48 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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Summary DOMESTIC HOT WATER
• DHW is the second-largest component of a multifamily building’s energy cost. • Water heaters may be stand-alone units or be integrated into the building’s heating system. • The goal is to provide everyone with water that is at least 110°F. • Recirculating systems can save water and heating energy, but constantly running pumps use energy. • Thermostatic mixing valves fail in the HOT position; electronic mixing valves fail in the COLD position. • Measure flow, leaks, temperature, and pressure to accurately diagnose and address DHW issues. • Tremendous energy savings can be had by adding low-flow fixtures and aerators, repairing leaks, adding pipe insulation, improving DHW makers, and changing recirculation systems. 49 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – January 2011
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