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Title: LOW COST HEAT PUMP WATER HEATER (HPWH)

Abstract

Water heating accounts for the second largest portion of residential building energy consumption, after space conditioning. Existing HPWH products are a technical success, with demonstrated energy savings of 50% or more compared with standard electric resistance water heaters. However, current HPWHs available on the market cost an average of $1000 or more, which is too expensive for significant market penetration. What is needed is a method to reduce the first cost of HPWHs, so that the payback period will be reduced from 8 years to a period short enough for the market to accept this technology. A second problem with most existing HPWH products is the reliability issue associated with the pump and water loop needed to circulate cool water from the storage tank to the HPWH condenser. Existing integral HPWHs have the condenser wrapped around the water tank and thus avoid the pump and circulation issues but require a relatively complex and expensive manufacturing process. A more straightforward potentially less costly approach to the integral, single package HPWH design is to insert the condenser directly into the storage tank, or immersed direct heat exchanger (IDX). Initial development of an IDX HPWH met technical performance goals, achieving measured efficiencies ormore » energy factors (EF) in excess of 1.79. In comparison conventional electric water heaters (EWH) have EFs of about 0.9. However, the initial approach required a 2.5" hole on top of the tank for insertion of the condenser - much larger than the standard openings typically provided. Interactions with water heater manufacturers indicated that the non standard hole size would likely lead to increased manufacturing costs (at least initially) and largely eliminate any cost advantage of the IDX approach. Recently we have been evaluating an approach to allow use of a standard tank hole size for insertion of the IDX condenser. Laboratory tests of a prototype have yielded an EF of 2.02.« less

Authors:
 [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Building Technologies Research and Integration Center (BTRIC)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
930738
DOE Contract Number:
AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: International Refrigeration and Air Conditioning Conference at Purdue University, West Lafayette, IN, USA, 20060717, 20060720
Country of Publication:
United States
Language:
English
Subject:
heat pump water heater; immersed condenser

Citation Formats

Mei, Vince C, and Baxter, Van D. LOW COST HEAT PUMP WATER HEATER (HPWH). United States: N. p., 2006. Web.
Mei, Vince C, & Baxter, Van D. LOW COST HEAT PUMP WATER HEATER (HPWH). United States.
Mei, Vince C, and Baxter, Van D. Sun . "LOW COST HEAT PUMP WATER HEATER (HPWH)". United States. doi:.
@article{osti_930738,
title = {LOW COST HEAT PUMP WATER HEATER (HPWH)},
author = {Mei, Vince C and Baxter, Van D},
abstractNote = {Water heating accounts for the second largest portion of residential building energy consumption, after space conditioning. Existing HPWH products are a technical success, with demonstrated energy savings of 50% or more compared with standard electric resistance water heaters. However, current HPWHs available on the market cost an average of $1000 or more, which is too expensive for significant market penetration. What is needed is a method to reduce the first cost of HPWHs, so that the payback period will be reduced from 8 years to a period short enough for the market to accept this technology. A second problem with most existing HPWH products is the reliability issue associated with the pump and water loop needed to circulate cool water from the storage tank to the HPWH condenser. Existing integral HPWHs have the condenser wrapped around the water tank and thus avoid the pump and circulation issues but require a relatively complex and expensive manufacturing process. A more straightforward potentially less costly approach to the integral, single package HPWH design is to insert the condenser directly into the storage tank, or immersed direct heat exchanger (IDX). Initial development of an IDX HPWH met technical performance goals, achieving measured efficiencies or energy factors (EF) in excess of 1.79. In comparison conventional electric water heaters (EWH) have EFs of about 0.9. However, the initial approach required a 2.5" hole on top of the tank for insertion of the condenser - much larger than the standard openings typically provided. Interactions with water heater manufacturers indicated that the non standard hole size would likely lead to increased manufacturing costs (at least initially) and largely eliminate any cost advantage of the IDX approach. Recently we have been evaluating an approach to allow use of a standard tank hole size for insertion of the IDX condenser. Laboratory tests of a prototype have yielded an EF of 2.02.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

Conference:
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  • Air source heat pump water heaters (HPWHs) have been available in the US since the early 1980s, but never reached annual sales greater than 10,000 units. While HPWHs can offer energy savings of as much as 67% over conventional electric resistance water heaters, their relatively high first cost has kept them from obtaining significant market penetration. In order to bring the energy savings benefits of HPWHs to the general water heating market, it is essential to substantially reduce the installed cost. This paper describes the development of a new heat pump water heater designed to provide reasonable energy efficiency atmore » a substantially reduced first cost. Water heating simulations, conducted using the WATSIM analysis tool, showed that a significant amount of the typical consumer's hot water demand could be met using a reduced-capacity heat pump, with the balance of demand being met by supplemental electric resistance heating. Reducing the capacity of the heat pump offers several advantages including lower first cost and reduced impact on space heating. The goal of the present development effort was to substantiate a low-cost HPWH design approach in preparation for a broader product and market development initiative. The design approach was put into practice by modifying a conventional 300 liter (80-gallon) electric water heater. Proof-of-principle laboratory tests were successfully conducted verifying initial performance estimates. The prototype unit was then installed in a five-person household in new England for an extended field test. The unit reliability met the test family's hot water needs throughout the fall, winter and spring and continues to operate.« less
  • DOE has supported efforts for many years with the objective of getting a water heater that uses heat pump technology (aka a heat pump water heater or HPWH) successfully on the residential equipment market. The most recent previous effort (1999-2002) produced a product that performed very well in ORNL-led accelerated durability and field tests. The commercial partner for this effort, Enviromaster International (EMI), introduced the product to the market under the trade name Watter$aver in 2002 but ceased production in 2005 due to low sales. A combination of high sales price and lack of any significant infrastructure for service aftermore » the sale were the principal reasons for the failure of this effort. What was needed for market success was a commercial partner with the manufacturing and market distribution capability necessary to allow economies of scale to lead to a viable unit price together with a strong customer service infrastructure. General Electric certainly meets these requirements, and knowing of ORNL s expertise in this area, approached ORNL with the proposal to partner in a CRADA to produce a high efficiency electric water heater. A CRADA with GE was initiated early in Fiscal Year, 2008. GE initially named its product the Hybrid Electric Water Heater (HEWH).« less
  • Until now the heat pump water heater (HPWH) has been a technical success but a market failure because of its high initial cost. Oak Ridge National Laboratory (ORNL) was tasked to examine commercially available HPWH product technology and manufacturing processes for cost saving opportunities. ORNL was also tasked to verify the technical feasibility of the cost saving opportunities where necessary and appropriate. The objective was to retain most of the HPWH s energy saving performance while reducing cost and simple payback period to approximately three years in a residential application. Several cost saving opportunities were found. Immersing the HPWH condensermore » directly into the tank allowed the water-circulating pump to be eliminated and a standard electric resistance storage water heater to be used. In addition, designs could be based on refrigerator compressors. Standard water heaters and refrigerator compressors are both reliable, mass produced, and low cost. To verify the feasibility of these cost saving measures, ORNL completed a conceptual design for an HPWH based on an immersed condenser coil that could be directly inserted into a standard water heater tank through a sleeve affixed to one of the standard penetrations at the top of the tank. The sleeve contour causes the bayonet-style condenser to helix while being pushed into the tank, enabling a condenser of sufficient heat transfer surface area to be inserted. Based on this design, ORNL fabricated the first laboratory prototype and completed preliminary laboratory tests in accordance with the DOE Simulated Use Test Procedure. Hardening during double-wall condenser fabrication was not overcome, so the prototype is single-walled with a liner. The prototype unit was found to have an energy factor of 2.02, verifying that the low-cost design retains most of the HPWH s energy saving performance. Industry involvement is being sought to resolve the fabrication issue and quantify progress on reducing cost and simple payback period to approximately three years in a residential application. This report provides information on the design, prototype construction, laboratory test data, and analyses of this HPWH.« less
  • Since the 1980s various attempts have been made to apply the efficiency of heat pumps to water heating. The products generated in the 80s and 90s were not successful, due in part to a lack of reliability and difficulties with installation and servicing. At the turn of the century, EnvironMaster International (EMI) produced a heat pump water heater (HPWH) based on a design developed by Arthur D. Little (ADL), with subsequent developmental assistance from Oak Ridge National Laboratory (ORNL) and ADL. This design was a drop-in replacement for conventional electric water heaters. In field and durability testing conducted by ORNL,more » it proved to be reliable and saved on average more than 50% of the energy used by the best conventional electric water heater. However, the retail price set by EMI was very high, and it failed in the market. ORNL was tasked to examine commercially available HPWH product technology and manufacturing processes for cost saving opportunities. Several cost saving opportunities were found. To verify the feasibility of these cost saving measures, ORNL completed a conceptual design for an HPWH based on an immersed condenser coil that could be directly inserted into a standard water tank through a sleeve affixed to one of the standard penetrations at the top of the tank. After some experimentation, a prototype unit was built with a double-wall coil inserted into the tank. When tested it achieved an energy factor (EF) of 2.12 to 2.2 using DOE-specified test procedures. A.O. Smith contacted ORNL in May 2006 expressing their interest in the ORNL design. The prototype unit was shipped to A.O. Smith to be tested in their laboratory. After they completed their test, ORNL analyzed the raw test data provided by A.O. Smith and calculated the EF to be approximately 1.92. The electric resistance heating elements of a conventional electric water heater are typically retained in a heat pump water heater to provide auxiliary heating capacity in periods of high demand. A.O. Smith informed us that when they applied electric resistance backup heating, using the criterion that resistance heat would be applied whenever the upper thermostat saw water temperatures below the heater s nominal setpoint of 135oF, they found that the EF dropped to approximately 1.5. This is an extremely conservative criterion for backup resistance heating. In a field test of the previously mentioned EMI heat pump water heater, residential consumers found satisfactory performance when the criterion for use of electric resistance backup heating was the upper temperature dropping below the set point minus 27 degrees. Applying this less conservative criterion to the raw data from the original A.O. Smith EF tests indicates that electric resistance heating would never have come on during the test, and thus the EF would have remained in the vicinity of 1.9. A.O. Smith expressed concern about having an EF below 2, as that value triggers certain tax advantages and would assist in their marketing of the product. We believe that insertion of additional length of tubing plus a less conservative set point for electric resistance backup heating would remedy this concern. However, as of this writing, A.O. Smith has not decided to proceed with a commercial product.« less
  • A research project was conducted to investigate the effect of homeowner installable devices on total energy used, hourly maximum demand and spread of the demand over a monthly time period. Groups of houses representative of substation scale loading had heat pump and water heater controls installed. The major results obtained were: 1) the microprocessor based thermostats significantly reduced the total energy used and the maximum demand, 2) the outdoor heat pump thermostats significantly reduced the total energy used and the maximum demand, and 3) the time clocks on the lower water heater elements reduced the usage and the maximum demand.