Transcribe NRG

Recommended DHW Tasks:

N-now DHW tasks
Install Water-Efficient Showerheads and Faucet Aerators
Insulate Hot Water Tanks and Pipes
Convert Laundry to Cold Rinse

R-research DHW tasks
Install Hot Water Off-Peak Controls
Replace Inefficient Water Heating Equipment or Systems
Install Condenser Heat-Recovery Equipment

G-green DHW task
Install Solar Water Heater System

DHW - Overview

Estimating hot water usage in a home is difficult because of the wide differences in water use habits. However, water heating costs can always be reduced with conservation measures and water heating alternatives. Water heaters come in a range of efficiencies, warranties, and fuel sources. Their efficiencies are measured by a rating known as the Energy Factor (EF). The energy factor is a measure of the overall efficiency of a water heater and includes recovery efficiency, standby losses, and cycling losses.

In addition to variations in insulation, gas water heater efficiency is also affected by burner design, the shape of the flue baffles that slow the hot exhaust gases down to increase heat transfer to the water, and the amount of surface area between the flue gases and the water. Energy Factors (EF) for Gas Water Heaters can be below 0.62 for older storage type water heaters. Higher efficiency gas water heaters have blowers for venting and delivery of combustion air and more sophisticated energy features, such as electronic ignition, flue dampers, and condensing heat exchangers. These high efficiency gas water heaters can achieve energy factors over 0.90. For electric water heaters, higher efficiency units have energy factors up to 0.97. Often, the additional cost of a high efficiency unit is quite low compared to the savings. ENERGY STAR labeling for electric water heaters is not available because, beyond adding additional insulation to reduce standby losses, little can be done to improve efficiency. In general, electric hot water heaters are more expensive to operate than gas units; however, depending on usage and the difference between electricity and gas prices this difference can be small.

DHW - Easy Conservation Measures

Easy cost savings can be obtained by: repairing leaky faucets; reducing temperature settings; adding an insulating wrap to an older water heater; install high efficiency low-flow showerheads; washing clothes in cold water when possible; and replacing your old water heater when it fails with a more efficient model.

Heat Pump Water Heaters

Heat pump water heaters use electricity to move heat from one place to another instead of generating heat directly. As a result, they can be two to three times more energy efficient than conventional electric resistance water heaters. You can purchase a stand-alone heat pump water heating system as an integrated unit with a built-in water storage tank and back-up resistance heating elements. Note: Heat pump water heaters will not operate efficiently in a cold space and they tend to cool the spaces they are in. Because they remove heat from the air, any type of air-source heat pump system works more efficiently in warmer conditions.

DHW - Condenser Heat Recovery

A heat recovery unit can be installed to recover the concentrated high temperature heat from your air conditioner (or heat pump) condenser circuit and use it to heat the water in your hot water tank. This will provide free hot water heating during the season that the air conditioner operates and is therefore an excellent return on investment for residential customers located in areas where the air conditioner is running the majority of the year. Alternatively, a solar hot water system can be used to provide hot water. However, installing a heat recovery unit to capture waste heat from your HVAC condenser has advantages like operating day or night, rain or shine, with no solar panels on the roof and it is maintenance free. Another advantage of a condenser heat recovery unit is that it lowers the head pressure of the compressor, which improves the efficiency of your existing HVAC system and provides an additional air-conditioning savings of 10 to 20%.

DHW - Instantaneous Water Heaters

Instantaneous (also call On Demand) water heaters use higher capacity electric coils or gas burners to heat cold water only when there is a need for hot water. Note: Electric units use a large amount of current and may require special wiring. These water heaters save energy in two ways: they have no storage tank so there is no need to keep stored water continuously warm, and gas-fired units usually heat water more efficiently than gas tank type water heaters. By reducing or eliminating the standby losses and by increasing efficiency, on demand water heaters may save 20% or more of an annual water heating bill. Instantaneous water heaters must be sized carefully for their planned use. A small unit may provide hot water for only one faucet or appliance at a time. Several units are generally needed to provide hot water for conventional residential uses, which makes installing instantaneous water heaters cost prohibitive in most houses.

DHW - Solar Water Heaters

Solar water heaters are typically installed and maintained by someone with experience in that field. With energy and tax incentives at the state and federal level, solar water heaters can be a cost effective option. The incorporation of a domestic solar hot water system into residential homes has become increasingly popular over the last several years. The basic concept of solar hot water systems is to use energy from the sun to heat (or preheat) water, thereby reducing the gas or electric requirements to produce hot water.

In general, all solar hot water systems have a solar collector (to collect energy from the sun), and a storage tank (to store the hot water). From this, the solar-thermal systems can be separated into two different categories, active and passive systems. Active solar-thermal systems rely on pumps and valves to circulate the water or heat exchange fluid through the solar collector, while passive solar-thermal systems rely on the natural tendency of water to rise when heated, and thereby circulate through the system. While active systems are slightly more complicated than passive systems, they can be more flexible in terms of the placement of the components since the location of the storage tank is not dependent on the physics of hot water buoyancy. On the other hand, passive systems, because of the lack of pumps, are usually more durable and less prone to problems. With recent advances in thin-film solar cells, the use photovoltaics to power electric hot water heaters is gaining popularity compared to these traditional solar-thermal options. Note: To be effective, solar water heaters must be installed in a geographic location that receives sufficient sunlight and collectors (or photovoltaic panels) must be installed in a location free of shading.