Water bills are not the only operating cost associated with plumbing systems. They also involve energy costs, in the form of pumping and heating water. A well-designed plumbing installation has optimal capacity, which prevents oversized pipes and equipment. Smaller booster pumps and water heaters have a lower initial cost and operating cost.
A well-designed plumbing system is also less prone to equipment breakdowns and failures, avoiding repairs and replacement of components that can be highly harmful to tenants.
Water efficiency starts with plumbing fixtures
The first step to providing a high-performance plumbing system is to select water-efficient fixtures. The U.S. Environmental Protection Agency created the WaterSense Labeling Program for low-flow plumbing fixtures, which simplifies product specification. The savings from a single high-performance fixture may seem small, but it adds up when you're dealing with hundreds of them in a tall building. The US EPA's WaterSense program covers the following categories of plumbing fixtures:
- Residential bathrooms
- Showers
- Bathroom Faucets
- Commercial bathrooms
- Urinals
- Pre-rinse spray valves
- Irrigation Controllers
- Spray sprinkler bodies
Please remember that this list is not definitive as new product categories are being reviewed. As of June 2018, the US EPA is also developing WaterSense labeling requirements for water softeners, soil moisture-based controllers, and bathtub and shower diverters.
Plumbing risers and branches
Piping selection also influences energy efficiency. Plumbing systems with smaller pipes have a lower initial cost simply because the pipes and fittings use less material, but this also increases pressure loss due to internal friction. As a result, you need more pumping power to overcome pipeline losses.
On the other hand, pipes with a larger diameter have reduced friction losses. However, there is an upper limit to the size of a pipe: larger pipes and fittings cost more, and an excessively wide pipe results in slower water speed. This can be a problem if you want to supply hot water from the basement to the upper floor of a high-rise building.
The best recommendation for having optimally sized piping is to work with qualified design professionals. They can specify pipe diameters that minimize pressure losses due to friction without being excessively expensive.
Optimizing Water Booster Pumps
Municipal water pressure is sufficient for properties with a few floors, but it is necessary to use water booster pumps in the construction of skyscrapers. As they run on electricity and the kWh in New York and New Jersey are very high, it pays to design the system as efficiently as possible.
To reduce pump motor running costs, two energy efficiency measures are recommended:
- Using a NEMA Premium Efficiency motor with the right power.
- Controlling motor speed with a frequency inverter (VFD).
The water booster pump must be specified so that the inlet pressure does not fall below the net positive suction head (NPSH). This prevents cavitation, a phenomenon in which the pump impeller is worn out by the formation and implosion of bubbles. It is also a good idea to install the pump at the lowest possible level of the building, where the static pressure is highest.
Efficient Water Heating
Domestic hot water systems are available in a wide range of configurations.
- Natural gas and heating oil are commonly used as heat sources, although efficient heat pumps can offer economical heating without the emissions of combustion heaters.
- In terms of physical characteristics, water heating systems may or may not have a storage tank.
- There are also indirect systems that extract heat from the space heating boiler or furnace, through a heat exchanger or tankless coil.
Regardless of your heating system configuration, saving water saves energy for the simple reason that fewer gallons pass through your heating system throughout the year. Of course, additional savings can also be achieved by modernizing the domestic hot water system. The lowest operating cost is typically achieved with tankless gas heaters and high-efficiency heat pumps. Electric resistance heaters are typically not recommended in New York and New Jersey due to high kWh prices.
Conclusion
Energy efficiency measures often focus on HVAC and lighting systems, and solar energy has received a lot of attention lately thanks to the reduced cost of photovoltaic modules. However, there are also many opportunities to reduce building operating costs with effective plumbing design. This saves not only water, but also electricity and heating fuels – municipal water supplies do not always have the correct pressure and temperature, which makes water pumping and heating systems necessary.
