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Ask the Expert: Domestic Hot Water O&Ms and FIMs

Posted by Danielle Marquis

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October 22, 2015 at 6:24 AM

Question: How can I improve the energy efficiency of my facility's domestic hot water system?

 

ATE-Bill-BW 

 

Answer: Domestic hot water system issues, which include problems with leaks and temperature control, can take several forms. An energy audit will typically identify energy inefficiencies in one or several of the following areas:

 

  • Hot water temperature is excessive
  • System insulation is damaged or missing
  • Water temperatures are not reduced during unoccupied periods
  • Water drips or leaks are evident
  • Heat pump water heater coils are not maintained on a scheduled basis
  • Hot water recirculating pumps run continuously
  • Electric water heater has no time restrictions on heating cycle
  • Devices to conserve heated water have not been utilized where practical
  • Storage tanks, piping and water heaters are used inefficiently

 

The suggested operations and maintenance ("O&M") improvements and facility improvement measures ("FIM") will vary based on your facility's unique mix of inefficiencies, but what follows are some general guidelines.

 


Suggested Domestic Hot Water O&Ms:

 

  • Lower thermostat or controller set point to 105-115 degrees Fahrenheit for general purposes. Consult appropriate codes and regulations for permissible water temperatures for sanitation, health and medical purposes.
  • Repair or replace damaged or missing insulation. Protect as necessary to prevent recurrence of damage.
  • Schedule setbacks (either manually or with an existing time clock). Consider schedule's impact on electrical demand.
  • Repair leaks and defective faucets and pumps
  • Schedule heat pump water heater coil maintenance following manufacturer's recommendations.
  • Develop operating schedule to match occupancy.
  • Utilize "vacation cycle" on water heater when not needed during extended periods (Note: Complete deactivation can cause leaks).

 

Suggested Domestic Hot Water FIMs:

 

  • Install an appropriate automatic water temperature control device.
  • Limit the duty cycle with a time clock or other control devices to avoid adding the water heating load to the building during peak electrical demand periods (additional hot water storage capacity may be required).
  • Install mixing valves.
  • Replace standard faucets with self-closing, flow restrictor valves (Note: Highly mineralized water or water containing sediment can cause blockages).
  • Install a solar water heater to assist in meating hot water demand. This will reduce significantly the consumption of traditional energy fuels in facilities which are large users of hot water.
  • Install a small domestic hot water heater to maintain desired water temperature in water storage tank. This could eliminate the need for operating one of the large space heating boilers during summer months.
  • Install de-centralized water heating.

 

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