Energy-Efficient Hot Water Systems

Hot water production and transport systems have been used for several decades in residential, commercial and industrial buildings. The applications are numerous. From domestic hot water production to heating and industrial processes, a significant amount of energy is devoted to hot water production. The efficiency of these systems depends primarily on their design.

Description of hot water systems

In heating, a hot water system consists of a few components such as the source (the appliance(s) that heat the water), the distribution system (the piping) and the terminals (the appliances that transfer the heat to the room, e.g. radiators). There are many different types of sources. Water is often heated by boilers, either electric or gas. Other possible sources are: solar energy, geothermal energy, heat pumps or heat recovery from refrigeration processes.

The design of hot water systems

In order for these systems to meet the demand while consuming the minimum amount of energy possible, several design parameters must be considered. It will be important for the engineer designing the system to consider operating temperatures, pressures and flow rates, the amount of hot water required, pipe run distances, and water quality.

If a system is poorly designed, there will be significant losses in both water and energy. For example, undersized or oversized water pipes will make a system much less efficient, hence the importance of optimal selection and design to heat water to its optimum point. It is important that the designer works with the client to design a system that will meet his needs while reducing capital and operating costs.

Optimization of hot water systems at the design stage

Selecting a high efficiency heat source is an obvious step in designing an efficient system. However, it will not be of much use if some of the heat produced is lost in distribution before reaching the terminals. When designing the system, it will be important to ensure that 1) the length of the pipes between the source and the terminals is as short as possible and 2) that they are insulated. If these losses are minimized, the required water flow will also be reduced. As a result, the power of the pumps and the energy required to operate them can also be reduced.

Pipe insulation

Some recent studies have shown that poorly insulated or uninsulated piping causes very high energy losses. According to the Hiller 2005A study, energy losses in a recirculation loop can reach 10% to 20% for a drinking water distribution system. Some installations suffer losses of up to 90%. The Canadian Energy Code for Buildings, the NECB, establishes insulation thicknesses that must be respected in order to reduce thermal losses due to the transport of hot water.

Proper pipe insulation is even more critical when pipes are buried. One study showed that an identical ¾” of insulation reduces heat loss by 94% in the case of buried pipe versus 50% when the pipe is exposed to the air. This difference is due to the fact that soil conducts heat much better than air, hence the importance of properly insulating underground pipes.

Conclusion

There are many opportunities to save energy consumed by hot water systems. This article covers only a few of them.

If you have a project in mind or if you wish to make your building more energy efficient and reduce your ecological footprint, contact us and the Ecovision Consultants team will be happy to assist you.

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