Residential heat pump water heaters (HPWHs) have recently reemerged on the U. S. market. These units have the potential to provide homeowners significant cost and energy savings. However, actual in-use performance of an HPWH will vary significantly with climate, installation location, HVAC equipment, and hot water use. In conditioned space, the cooling provided by the HPWH can be either a net benefit or a penalty depending on climate; in unconditioned space the ambient air temperature has a significant impact on its performance. To determine the in-use energy consumption of an HPWH in different regions, annual simulations of 50 and 80 gallon HPWHs as well as a standard electric resistance water heater installed in conditioned and unconditioned spaces were performed for more than 900 locations across the U. S. The simulations included a benchmark home to account for interactions between the space conditioning equipment and the HPWH and a realistic hot water draw profile that varied between 45 and 60 gallons per day with local mains water temperature. Results showed that the HPWH will always save some source energy compared to a standard electric water heater, although savings vary widely with location. In addition to source energy savings, the breakeven cost (the net installed cost an HPWH would have to have to be a cost neutral replacement for a standard water heater) was also examined. The highest breakeven costs were seen in cases with high energy savings, such as the Southeast, or high energy rates, such as New England and California. Although the breakeven cost is higher for the 80 gallon HPWH than for the 50 gallon HPWH, the 80 gallon unit's higher net installed costs makes it likely that the 50 gallon HPWH will be more cost effective.

Heat pump water heaters (HPWHs) have recently re-emerged in the U.S. residential water heating market and have the potential to provide homeowners with significant energy savings. However, there are questions as to the actual performance and energy savings potential of these units, in particular in regards to the heat pump's performance in unconditioned space and the impact of the heat pump on space heating and cooling loads when it is located in conditioned space. To help answer these questions, NREL performed simulations of a HPWH in both conditioned and unconditioned space at over 900 locations across the continental United States and Hawaii. Simulations included a Building America benchmark home so that any interaction between the HPWH and the home's HVAC equipment could be captured. Comparisons were performed to typical gas and electric water heaters to determine the energy savings potential and cost effectiveness of a HPWH relative to these technologies. HPWHs were found to have a significant source energy savings potential when replacing typical electric water heaters, but only saved source energy relative to gas water heater in the most favorable installation locations in the southern United States. When replacing an electric water heater, the HPWH is likely to break even in California, the southern United States, and parts of the northeast in most situations. However, the HPWH will only break even when replacing a gas water heater in a few southern states.

Renewable energy sources – including biomass, geothermal, ocean, solar, and wind energy, as well as hydropower – have a huge potential to provide energy services for the world. The renewable energy resource base is sufficient to meet several times the present world energy demand and potentially even 10 to 100 times this demand. This chapter includes an in-depth examination of technologies to convert these renewable energy sources to energy carriers that can be used to fulfill our energy needs, including their installed capacity, the amount of energy carriers they produced in 2009, the current state of market and technology development, their economic and financial feasibility in 2009 and in the near future, as well as major issues they may face relative to their sustainability or implementation.

The market environment for solar water heating technology has changed substantially with the successful introduction of heat pump water heaters (HPWHs). The addition of this energy-efficient technology to the market increases direct competition with solar water heaters (SWHs) for available energy savings. It is therefore essential to understand which segment of the market is best suited for HPWHsand focus the development of innovative, low-cost SWHs in the market segment where the largest opportunities exist. To evaluate cost and performance tradeoffs between high performance hot water heating systems, annual energy simulations were run using the program, TRNSYS, and analysis was performed to compare the energy savings associated with HPWH and SWH technologies to conventional methods ofwater heating.

NREL has developed the novel concept of a desiccant enhanced evaporative air conditioner (DEVap) with the objective of combining the benefits of liquid desiccant and evaporative cooling technologies into an innovative 'cooling core.' Liquid desiccant technologies have extraordinary dehumidification potential, but require an efficient cooling sink. DEVap's thermodynamic potential overcomes manyshortcomings of standard refrigeration-based direct expansion cooling. DEVap decouples cooling and dehumidification performance, which results in independent temperature and humidity control. The energy input is largely switched away from electricity to low-grade thermal energy that can be sourced from fuels such as natural gas, waste heat, solar, or biofuels.

This paper studies a collector design that utilizes unglazed photovoltaic/thermal (PV/T) collectors preheating air for glazed air heating modules. The performance modeling of these collectors is examined both individually and in series. For each collector type, a dynamic, finite difference, first-law model has been created using literature correlations for friction. The models were compared to performance data, calibrating the models by scaling of friction terms for best fit. The calibrated models generally agree well with the experimental data; even during sudden changes to ambient conditions. The root mean square error between the unglazed PV/T model and experiment results for the useful thermal energy gain and the outlet air temperature are 7.12 W/m2 and 1.07°C, respectively. The annual source energy performance of the building-integrated PV/T (BIPV/T) array is then simulated for residential applications in seven climate zones of the United States of America. The performance of the BIPV/T array is characterized by the amount of net electrical energy and useful thermal energy produced. The useful thermal energy is defined as the amount of energy offset by the BIPV/T system for water heating and space conditioning. A BIPV/T system composed 87.5% of PV modules, and 12.5% of glazed air heating modules, offsets the same amount of source energy as a roof-mounted PV system of the same area. This array composition increases the thermal energy gain by 47% over a BIPV/T array composed solely of PV modules.

In May 2007, Forest City Military Communities won a US Department of Energy Solar America Showcase Award. As part of this award, executives and staff from Forest City Military Communities worked side-by-side with a DOE technical assistance team to overcome technical obstacles encountered by this large-scale real estate developer and manager. This paper describes the solar technical assistance that was provided and the key solar experiences acquired by Forest City Military Communities over an 18 month period.

The Florida Solar Energy Center (FSEC), with the support of the National Renewable Energy Laboratory, has investigated the thermal performance of solar absorbers that are an integral, yet indistinguishable, part of a building's roof. The first roof-integrated solar absorber (RISA) system was retrofitted into FSEC's Flexible Roof Facility in Cocoa, Florida, in September 1998. This ''proof-of-concept'' system uses the asphalt shingle roof surface and the plywood decking under the shingles as an unglazed solar absorber. Data was gathered for a one-year period on the system performance. In Phase 2, two more RISA prototypes were constructed and submitted for testing. The first used the asphalt shingles on the roof surface with the tubing mounted on the underside of the plywood decking. The second prototype used metal roofing panels over a plywood substrate and placed the polymer tubing between the plywood decking and the metal roofing. This paper takes a first look at the thermal performance results for the ''invisible'' solar absorbers that use the actual roof surface of a building for solar heat collection.

Four types of domestic hot water (DHW) systems installed in 80 homes throughout Florida are currently monitored by the Florida Solar Energy Center (FSEC) under a demonstration program for the Florida Public Service Commission. The data is analyzed to determine the average system efficiency and the time-of-day electricity demand profiles. For the last half of 1982 and the first two months of 1983, solar systems show the highest average efficiency and the lowest electrical load profile.

To achieve at least 50% reduction in cost of savings for residential solar water heaters (SWHs), polymer materials and manufacturing are being used, which also enable system redesign for parts reduction and easier installation. Two teams are bringing new low- cost systems to the market in FY 2007. Technical support at NREL for modeling and testing provided new models and test procedures for rating innovative integral-collector-storage (ICS) and thermosiphon (TS) systems. The pipe-freeze problem has been satisfactorily solved, enabling cold-climate TS systems. System analyses are under way for multi- function solar systems that affordably supply 100% of water heating, space heating, and space cooling, potentially enabling cost-neutral zero energy homes. 1. Objectives The low-cost SWH task in the Solar Heating and Lighting Subprogram has the objective to reduce the levelized cost of saved energy (LCOE) from SWH by at least 50%.