Tips for Properly Sizing a Submersible Water Well Pump
Water wells are a reliable, cost-effective way for homeowners to access a safe water supply. In fact, more than 42 million people in the United States use individual or private wells to supply water for their families. As more homeowners recognize the benefits of residential water wells, it’s important for contractors to know what goes into properly selecting and installing a residential water well system.
Jeff Smith, owner of Smith Well Drilling Inc. in eastern New York and a Goulds Water Technology dealer for over 35 years, is well-versed in proper residential well construction. Drawing on his extensive field experience, Smith shares key factors contractors need to consider to properly size a submersible well pump.
Selecting the Right Pump
Selecting or sizing the well pump is a critical step in the entire well construction process, and sizing is determined by the yield of the well and the needs of the household. The general rule is to never install a pump that has a greater capacity than the well.
“Start with the customer’s application and expectations,” Smith says. “A one-bathroom, two-bedroom household will have different needs than a four-bedroom, three-bathroom home.”
The pump usually refers to both the pump itself and an electric motor, which together make up the pumping unit. The pump may be one of several types: shallow or deep well jet, submersible or reciprocating. Along with the pump, a pressure tank is used to build up a reserve supply of water during times of high demand so the pump starts and stops less often. Less frequent cycling can prolong the life of a well pump.
Submersible pumps have become the choice for residential wells in recent years because they are highly efficient and capable of retrieving water from deeper depths — especially in areas where aquifers are deep underground.
Determining capacity: Residential water supply typically goes through daily cycles of high and low demand. The key to sizing a submersible well pump is to calculate the gallons per minute of water required during peak periods.
Smith recommends sizing a submersible well pump based on fixture count, which involves counting the fixtures and faucets in a home. The number of fixtures gives you the gallons per minute (gpm) required by the pump. All fixtures need to be counted, including kitchen, bath, laundry room, appliances, outside fixtures and any special fixtures like a pool or sprinkler system. For example, a house with two full bathrooms (sink, tub/shower, toilet), kitchen sink, basement sink, two outside faucets, washing machine and dishwasher would require a total of 12 gpm.
The rate at which water can be drawn from a residential well also needs to be considered.
“In terms of well yield, you need to figure out the capacity needed to meet peak demand when multiple fixtures are being used,” Smith says.
If peak demand exceeds the maximum amount of water available, the pump must be sized to fit the well’s capacity and the shortfall addressed through storage capacity.
Pipe size matters: Friction loss is the most overlooked factor in pump sizing and causes many systems to be improperly sized. Friction loss is the loss of pressure or head due to the resistance to flow in the pipe and fittings.
“Correct pipe sizing makes a difference,” Smith says. “The pipe needs to be big enough to minimize friction loss and achieve the proper rate of flow.”
He suggests following a standard rule of thumb that calls for using a minimum size pipe equal to the diameter of the discharge of the pump. For example, if your pump has 1¼-inch discharge, a minimum of 1¼-inch pipe should be used.
Maintain Constant Pressure
Contractors also need to take water pressure into account.
“People today want city-like water pressure and volume even if they live in rural areas,” Smith says.
Traditionally, fluctuating or inconsistent water pressure was an issue for residential water well systems. But with the advent of constant pressure systems, homeowners today can expect a constant, continuous flow of water whether they’re doing laundry, giving the kids a bath or watering the garden — or doing all of those things at once.
A constant pressure system operates with a variable frequency drive controller — like the Goulds Water Technology Aquavar SOLO2 — which monitors household water demands and adjusts pump speed to maintain constant pressure. Constant pressure systems also provide an additional layer of protection by monitoring for issues related to motor current draw, voltage, temperature and loss of pressure.
By providing pump and motor protection, variable frequency drive controllers reduce mechanical stress on well pumps, which minimizes the need for costly repairs. They also can reduce the energy consumption of a well pump and lower energy costs.