Water bills are not the only operating cost associated with plumbing systems. They also involve energy expenses, in the form of pumping and water heating. A well-designed plumbing installation has an optimal capacity, which avoids oversized piping and equipment. Smaller booster pumps and water heaters have both a lower upfront cost and a lower running cost.
A well-designed plumbing system is also less prone to breakdowns and equipment failure, avoiding reparations and component replacement that can be highly disruptive for tenants.
Water Efficiency Starts with Plumbing Fixtures
The first step to deliver a high-performance plumbing system is selecting fixtures with reduced water usage. The US Environmental Protection Agency has 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 they add up when you are dealing with hundreds of them in a high-rise building. The WaterSense program from the US EPA covers the following categories of plumbing fixtures:
Pre-Rinse Spray Valves
Spray Sprinkler Bodies
Keep in mind this list is not final, since 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 bath and shower diverters.
Plumbing Risers and Branch Lines
Pipe selection also influences energy efficiency. Plumbing systems with smaller pipes have a lower upfront cost, simply because the pipes and fittings use less material, but this also increases pressure loss due to internal friction. As a result, you require more pumping power to overcome piping losses.
On the other hand, pipes with a larger diameter have reduced friction losses. However, there is an upper limit to how large a pipe can be sized: larger pipes and fittings come with a higher cost, and an excessively wide pipe results in a slower water velocity. This can be an issue if you want to deliver hot water from the basement to the upper floor of a high-rise building.
The best recommendation to have optimally-sized piping is working with qualified design professionals. They can specify pipe diameters that minimize pressure losses due to friction, without being overly expensive.
Optimizing Water Booster Pumps
The pressure from the municipal water supply is enough for properties with few floors, but you need to use water booster pumps in high-rise construction. Since they run on electricity, and kWh in New York and New Jersey are very high, it pays off to design the system as efficient as possible.
To reduce the running costs of the pump motor, two energy efficiency measures are recommended:
Using a NEMA Premium Efficiency motor with the right horsepower.
Controlling motor speed with a variable frequency drive (VFD).
The water booster pump must be specified so that inlet pressure does not drop below the net positive suction head (NPSH). This prevents cavitation, a phenomenon where the pump impeller is worn down by the formation and implosion of bubbles. It is also a good idea to install the pump in the lowest possible building level, where static pressure is higher.
Natural gas and heating oil are commonly used as heat sources, although efficient heat pumps can offer cost-effective heating without the emissions of combustion heaters.
In terms of physical features, water heating systems can have a storage tank or can be tankless.
There are also indirect systems that draw 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 less gallons flow through the heating system during the year. Of course, there are additional savings to achieve by upgrading the domestic hot water system as well. The lowest operating cost is normally achieved with tankless gas heaters and high-efficiency heat pumps. Electric resistance heaters are not normally recommended in New York and New Jersey, due to the high kWh prices.
Energy efficiency measures often focus on HVAC and lighting systems, and solar power has received plenty 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 - the municipal water supply does not always have the right pressure and temperature, and this makes pumping and water heating systems necessary.
At New York EngineersChicago EngineersNew Jersey Engineers, we search for simple, eloquent solutions to complex problems. We minimize construction costs by eliminating the extraneous and focusing on the overall efficiency for the most streamlined designs.