This article discusses water heater or calorifier or geyser standby losses.

This discussion is part of a series of articles on how to improve the hot water pressure, quantity, flow, and water temperature safety in a building.

How to Reduce Standby Losses in Water Heaters

Water heater standby loss is defined as the amount of heat that is lost by a water heater when it is not in use or is in "standby" mode.

A water heater with comparatively high standby losses will be more-expensive to operate than one with lower standby losses, thus the cost of hot water used by building occupants will be higher when standby losses are higher.

Average [water heater] standby load for existing homes was found to be 1200 kWh/year, or approximately 26% of total energy consumed for water heating. (Pratt 1993).

A number of designs and features have been explored to reduce calorifier standby losses:

• Water heater insulation - provided standard by manufacturers of water heaters / geysers / calorifiers / hot water cylinders
  
  See INSULATE HOT WATER TANK?
• Water heater tank size - larger tanks give more total hot water quantity but have more surface area and greater standby loss
• Automatic flue dampers - installed on some gas or oil fired water heaters reduce standby losses
• Timers for electric water heaters - might reduce standby losses - though this point is argued below.
  
  See TIMERS for ELECTRIC WATER HEATERS
• Water heater type: tankless water heaters have no standby losses as the heater is not running when no hot water is being consumed
  
  See TANKLESS WATER HEATERS for details

Question: is it better to turn the water heater on and off to safe electricity?

2018/12/24 EG said:

I have older model AO Smith electric water heater in this apartment I moved into. Is it better to keep the power turn on or turn it on and off to conserve electricity?

This Q&A were posted originally at AO SMITH WATER HEATER AGE & MANUALS

Reply:

EG

You can turn off the water heater when leaving for several days or longer, and will save a little money - standby losses from modern electric water heaters are not so great that turning the heater off for a few hours saves you much money..

Conventional wisdom is that one can reduce the cost of electric hot water, if you use hot water at fairly regularly times, by having have an electrician install an automatic timer that turns the heater off for periods when it will not be in use -

see TIMERS for ELECTRIC WATER HEATERS

Interestingly, Elk and Auberg, in an un-dated report, found that timers don't save much energy, but that where hot water use occurs at regular times, turning the heater down (or maybe off) after the last daily use can save money. Here is an excerpt:

It is apparent that for no-flow standby loss reduction, the use of a clock-timer is marginal at best.

A more appropriate test sequence would be one which represents a typical household water use pattern, allowing the tank to be de-energized prior to the final hot water use during the day.

Under idealized conditions, the upper limit of savings achievable with a clock-timer would be to reduce standby losses to zero for the duration of the "off" time by completely using the last tankful of heated water.

A more realistic limit would be to use the last tankful down to about 100°F which would reduce the temperature differential to about 30 degrees over ambient the off period.

Other interesting facts about standby losses of water heaters:

Gas water heaters have higher standby losses than electric water heaters as additional heat from the water tank is lost through the exhaust flue (an automagic flue damper can reduce that loss)

Larger water heater tanks, because of their larger surface area, tend to have higher standby losses.

Tankless water heaters that do not maintain any reservoir of hot water have zero standby losses.

Research on Water Heater Standby Loss Costs & Reduction

• Aguilar, C., D.J. White, David L. Ryan, DOMESTIC WATER HEATING AND WATER HEATER ENERGY CONSUMPTION IN CANADA [PDF] (2005), CBEEDAC 2005–RP-02 retrieved 2018/12/25, original source: https://s3.amazonaws.com/academia.edu.documents/41744842/domwater_000.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1545757245&Signature=Q9rCX1pQCWuPJ7qxtZaLoj0JKMU%3D&response-content-disposition=inline%3B%20filename%3DDomestic_Water_Heating_and_Water_Heater.pdf
  Excerpt:
  
  Current domestic water heater standards and efficiencies are reviewed, and the various types of water heaters available, and the extent to which they are in use, are examined.
  
  Conventional tank water heater systems are by far the most common type of system used throughout Canada, although there is greater variation in water heater equipment in the Atlantic Provinces.
  
  In terms of information that is currently available, Pratt et al (1993) studied water heater standby consumption in the Pacific Northwest in the U.S.
  
  They found that single-family homes with electric space heating equipment consumed more than 4700 kWh/year to heat water for domestic uses.
  
  Average standby load for existing homes was found to be 1200 kWh/year, or approximately 26% of total energy consumed for water heating.
  
  Homes built as part of a Residential Standards Demonstration Program, which are presumably more energy efficient, averaged 1100 kWh/year (23%) in standby load, while a regional energy forecast for the same area assumes a standby load value of 1300 kWh/year (28%).
• Allard, Yannick, Michaël Kummert, Michel Bernier, Alain Moreau, INTERMODEL COMPARISON AND EXPERIMENTAL VALIDATION OF ELECTRICAL WATER HEATER MODELS IN TRNSYS Proceedings of Building Simulation 2011: 12th Conference of International Building Performance Simulation Association, Sydney, 14-16 November. Retrieved 2018.12.25 original source https://www.researchgate.net/profile/Alain_Moreau4/publication/280937720_Intermodel_comparison_and_experimental_validation_of_electrical_water_heater_models_in_TRNSYS/links/55ccd50908aebebb8f5779ac/Intermodel-comparison-and-experimental-validation-of-electrical-water-heater-models-in-TRNSYS.pdf
  
  Abstract:
  This study compares the performance of five electrical water heater models in the TRNSYS environment.
  
  The main capabilities, modeling assumptions and performance of the models are first assessed using an intermodel comparison.
  
  The main criteria for comparison are: domestic hot water supply temperature, power demand (time-dependent profile and overall energy use) and vertical temperature distribution in the tank.
  
  Experimental data are used to validate each model for one specific type of water heater and a selected water draw profile.
  
  Finally, the paper makes recommendations for selecting a model and configuring the model parameters in order to minimize the impact of modeling simplifications.
• Calvin W. Ek, P.E. and Co Douglas Auburg, PeE., CEM, ELECTRIC WATER HEATER STANDBY LOSSES: COMPARISON OF CONSERVATION STRATEGIES AND THEIR ENERGY SAVINGS [PDF] Bonneville Power Administration (un-dated), retrieved 2018/12/25, original source: aceee.org/files/proceedings/1984/data/papers/SS84_Panel5_Paper_06.pdf
• Cruickshank, Cynthia A., and Stephen J. Harrison. "Heat loss characteristics for a typical solar domestic hot water storage." Energy and Buildings 42, no. 10 (2010): 1703-1710.
• Du, Pengwei, and Ning Lu. "Appliance commitment for household load scheduling." IEEE transactions on Smart Grid 2, no. 2 (2011): 411-419.
  
  Abstract:
  This paper presents a novel appliance commitment algorithm that schedules thermostatically controlled household loads based on price and consumption forecasts considering users' comfort settings to meet an optimization objective such as minimum payment or maximum comfort. The formulation of an appliance commitment problem is described using an electrical water heater load as an example.
  
  The thermal dynamics of heating and coasting of the water heater load is modeled by physical models; random hot water consumption is modeled with statistical methods. The models are used to predict the appliance operation over the scheduling time horizon.
  
  User comfort is transformed to a set of linear constraints. Then, a novel linear-sequential-optimization-enhanced, multiloop algorithm is used to solve the appliance commitment problem. The simulation results demonstrate that the algorithm is fast, robust, and flexible.
  
  The algorithm can be used in home/building energy-management systems to help household owners or building managers to automatically create optimal load operation schedules based on different cost and comfort settings and compare cost/benefits among schedules.
• Fan, Jianhua, and Simon Furbo. "Buoyancy driven flow in a hot water tank due to standby heat loss." Solar Energy 86, no. 11 (2012): 3438-3449.
  
  Abstract
  
  Results of experimental and numerical investigations of thermal behavior in a vertical cylindrical hot water tank due to standby heat loss of the tank are presented. The effect of standby heat loss on temperature distribution in the tank is investigated experimentally on a slim 150 l tank with a height to diameter ratio of 5.
  
  A tank with uniform temperatures and with thermal stratification is studied.
  
  A detailed computational fluid dynamics (CFD) model of the tank is developed to calculate the natural convection flow in the tank. T
  
  he distribution of the heat loss coefficient for the different parts of the tank is measured by experiments and used as input to the CFD model.
  
  Water temperatures at different levels of the tank are measured and compared to CFD calculated temperatures. The investigations focus on validation of the CFD model and on understanding of the CFD calculations.
  
  The results show that the CFD model predicts satisfactorily water temperatures at different levels of the tank during cooling by standby heat loss.
  
  It is elucidated how the downward buoyancy driven flow along the tank wall is established by the heat loss from the tank sides and how the natural convection flow is influenced by water temperatures in the tank.
  
  When the temperature gradient in the tank is smaller than 2 K/m, there is a downward fluid velocity of 0.003–0.015 m/s.
  
  With the presence of thermal stratification the buoyancy driven flow is significantly reduced.
  
  The dependence of the velocity magnitude of the downward flow on temperature gradient is not influenced by the tank volume and is only slightly influenced by the tank height to tank diameter ratio.
  
  Based on results of the CFD calculations, an equation is determined to calculate the magnitude of the buoyancy driven flow along the tank wall for a given temperature gradient in the tank.
  
  Highlights
  
  Natural convection and thermal stratification in a hot water tank investigated.
  
  Measured water temperatures in the tank compared to CFD calculated temperatures.
  
  Heat loss from the tank sides helps to build up thermal stratification in the tank.
  
  A regression equation calculates velocity magnitude of flow along the tank sides.
  
  Influence of the tank height to diameter ratio and tank volume determined.
• Koomey, Jonathan G., Camilla Dunham, and James D. Lutz. "The effect of efficiency standards on water use and water-heating energy use in the US: A detailed end-use treatment." Energy 20, no. 7 (1995): 627-635.
• Lane, I. E., and N. Beute. "A model of the domestic hot water load." IEEE transactions on power systems 11, no. 4 (1996): 1850-1855.
• Mayhorn, Ebony T., S. A. Parker, F. S. Chassin, S. H. Widder, and R. M. Pratt. Evaluation of the demand response performance of large capacity electric water heaters. Pacific Northwest National Laboratory, 2015.
• Pratt, R. G., B. A. Ross, and W. F. Sandusky. "Analysis of water heater standby energy consumption from ELCAP homes." Energy and buildings 19, no. 3 (1993): 221-234.
  Abstract:
  
  The Bonneville Power Administration (Bonneville) routinely prepares forecasts of future energy demands in the Pacific Northwest region of the United States. Bonneville also implements conservation programs to reduce load demands.
  
  Results from the End-Use Load and Consumer Assessment Program (ELCAP), undertaken by the Pacific Northwest Laboratory for Bonneville, indicated that single-family homes with electric space-heating equipment consume more than 4700 kWh/yr to heat water for domestic uses.
  
  This energy use amounts to about 23% of the total electricity consumed. Additionally, the peak consumption for water heating coincides with regional system peak demands.
  
  Detailed analyses of the water heating end-use data acquired for residential buildings in ELCAP reveal that the average standby load for existing homes is 1200 kWh/yr, while homes built as part of the Residential Standards Demonstration Program averaged 1100 kWh/yr.
  
  These figures are consistent with the current figure of 1300 kWh/yr that is being used in the regional energy forecast.
  
  We also determined that standby loads for some of the participants were behaviorally driven. The data indicated the occurrence of vacancy setbacks in which the participant appears to lower the thermostat to save energy while the house is vacant.
  
  Anecdotal evidence from interviews revealed that this does occur. Reasons for setting back the thermostat ranged from not thinking about using the breaker, to fear that the tank would freeze in cold weather.
  
  These types of activities also appear to create the occurrence of dueling thermostats where the upper and lower thermostats, after the vacancy period, are not returned to the same temperature. This leads to additional energy use in an attempt to maintain a uniform temperature in the tank.
• Pratt, R. G., and B. A. Ross. MEASURED ELECTRIC HOT WATER STANDBY AND DEMAND LOADS FROM PACIFIC NORTHWEST HOMES. END-USE LOAD AND CONSUMER ASSESSMENT PROGRAM [PDF] No. PNL-7889. Pacific Northwest Lab., Richland, WA (United States), 1991.
  Abstract:
  
  The Bonneville Power Administration began the End-Use Load and Consumer Assessment Program (ELCAP) in 1983 to obtain metered hourly end-use consumption data for a large sample of new and existing residential and commercial buildings in the Pacific Northwest.
  
  Loads and load shapes from the first 3 years of data fro each of several ELCAP residential studies representing various segments of the housing population have been summarized by Pratt et al.
  
  The analysis reported here uses the ELCAP data to investigate in much greater detail the relationship of key occupant and tank characteristics to the consumption of electricity for water heating.
  
  The hourly data collected provides opportunities to understand electricity consumption for heating water and to examine assumptions about water heating that are critical to load forecasting and conservation resource assessments. Specific objectives of this analysis are to:
  
  (A) determine the current baseline for standby heat losses by determining the standby heat loss of each hot water tank in the sample,
  
  (B) examine key assumptions affecting standby heat losses such as hot water temperatures and tank sizes and locations,
  
  (C) estimate, where possible, impacts on standby heat losses by conservation measures such as insulating tank wraps, pipe wraps, anticonvection valves or traps, and insulating bottom boards,
  
  (D) estimate the EF-factors used by the federal efficiency standards and the nominal R-values of the tanks in the sample,
  
  (E) develop estimates of demand for hot water for each home in the sample by subtracting the standby load from the total hot water load,
  
  (F) examine the relationship between the ages and number of occupants and the hot water demand,
  
  (G) place the standby and demand components of water heating electricity consumption in perspective with the total hot water load and load shape.
• Sowmy, Daniel Setrak, and Racine TA Prado. "Assessment of energy efficiency in electric storage water heaters." Energy and Buildings 40, no. 12 (2008): 2128-2132.
  Abstract:
  Nowadays there are several ways of supplying hot water for showers in residential buildings. One of them is the use of electric storage water heaters (boilers).
  
  This equipment raises the water temperature in a reservoir (tank) using the heat generated by an electric resistance.
  
  The behavior of this equipment in Brazil is still a research object and there is not a standard in the country to regulate its efficiency. In this context, an experimental program was conducted aiming to collect power consumption data to evaluate its performance.
  
  The boilers underwent an operation cycle to simulate a usage condition aiming to collect parameters for calculating the efficiency. This 1-day cycle was composed of the following phases: hot water withdrawal, reheating and standby heat loss.
  
  The methods allowed the identification of different parameters concerning the boilers work, such as: standby heat loss in 24 h, hot water withdrawal rate, reheating time and energy efficiency. The average energy efficiency obtained was of 75%. The lowest efficiency was of 62% for boiler 2 and the highest was of 85% for boiler 9.
• Taylor, Megan E., Keith G. Ritland, and R. G. Pratt. HOT WATER ELECTRIC ENERGY USE IN SINGLE-FAMILY RESIDENCES IN THE PACIFIC NORTHWEST: Regional End-Use Metering Project (REMP). No. DOE/BP-13795-27. USDOE Bonneville Power Administration, Portland, OR (United States). Office of Energy Resources, 1991. Retrieved 2018/12/25, original source: https://www.osti.gov/servlets/purl/5242541
  Abstract:
  
  The Office of Energy Resources of the Bonneville Power Administration carriers out generation and conservation resource planning. The analysis of historical trends in and determinants of energy consumption is carried out by the office's End-Use Research Section.
  
  The End-Use Research Section operates a comprehensive data collection program to provide pertinent information to support demand-side conservation planning, load forecasting, and conservation program development and delivery.
  
  Part of this on-going program, commonly known as the End-Use Load and Consumer Assessment Program (ELCAP), was recently renamed the Regional End-Use Metering Project (REMP) to reflect an emphasis on metering rather than analytical activities.
  
  REMP is designed to collect electricity usage data through direct monitoring of end-use loads in buildings in the residential and commercial sectors and is conducted for Bonneville by Pacific Northwest Laboratories (Battelle).
  
  The detailed summary information in this report is on energy used for water heaters in the residential sector and is based on data collected from September 1985 through December 1990 for 336 of the 499 REMP metered homes.
  
  Specific information is provided on annual loads averaged over the years and their variation across residences. Descriptions are given of use as associated with demographic and energy-related characteristics. Summaries are also provided for electricity use by each year, month, and daytype, as well as at peak hot water load and peak system times.
  
  This is the second residential report. This report focuses on a specific end use and adds detail to the first report. Subsequent reports are planned on other individual end uses or sets of end uses.
• Wulfinghoff, Donald R. Energy efficiency manual. Vol. 3936. Maryland: Energy Institute Press, 1999.

...

Continue reading  at HOT WATER EFFICIENCY IMPROVEMENT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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  • HOT WATER EFFICIENCY IMPROVEMENT
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  • WATER HEATER STANDBY LOSSES
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