Pumps Operations in the Building Envelope
Water flows downhill. Nothing could be more simple. Getting water to the top floor of an urban skyscraper is a bit more difficult. Mere gravity flow or even accumulated static pressure head aren’t sufficient to accomplish this task. Pumps are obviously needed. But what kinds of pumps are used in commercial and industrial buildings? A building designer will have to examine a wide variety of different pumps and their various applications.
Building Water Service Requirements, Flow Rates, and Pressure Heads
It’s all a question of height. Not just physical height, but applied pressure head measured in equivalent feet of water column. Converting pressure to equivalent water column height is a straight forward conversion involving the standard density of water. Water weighs approximately 62.4 pounds per cubic feet. Therefore, each foot of water height applies a pressure at the bottom of the column of 62.4 pounds per square foot, equivalent to 0.433 pounds per square inch. So 1 psi of pressure is equivalent to 2.307 feet (27.7 inches) of water column. But how much pressure is enough? According to the Uniform Plumbing Code, each fixture has a specified maximum flow rate and applied operating pressure.
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Effective pressure is a result of system pressure heads and the height of the building in question. A two-story building (ranging in height from 25 to 40 feet) can be adequately supplied by a typical water pipeline’s pressure head. Anything higher than that (a multi-story building) cannot be supplied by standard pressure in water supply systems and have to be augmented by a system of pumps and tanks to raise water to boost the water pressure inside of the building and raise the water to the top-most floor. The simplest configuration involves a single large water storage tank installed on top of the building roof that has been fed water by a booster pump located at the building’s water main connection. Water servicing the building then drains via gravity from the water storage tank to the floors and water fixtures in the building below.
Modern buildings utilize more sophisticated systems, which ironically can be easier to install. Many are prefabricated and can be installed onsite as skid-mounted units. Configurations can be customized to all for ease of installation in tight confines and awkward spaces. Systems are available that can cut energy bills by using variable speed controls. All of these new features, such as touch screen controls, an operational interface with other building systems such as lighting and HVAC, and self-diagnosing booster pumps, constitute what is referred to as smart pump technology.
How Booster Pumps Work—The Basics
Once the water arrives at the building’s water connection, it is the pump’s job to raise the water through the building service pipes to one or more temporary storage tanks to apply sufficient pressure for direct usage. A pump is defined as “a device that raises, transfers, delivers, or compresses fluids or that attenuates gases especially by suction or pressure or both.” It converts supplied electrical energy into mechanical energy, which in turn creates pressure head on the fluid it is pumping. The mechanical energy it creates can be imparted by a suction apparatus, impellor blades, or displacement piston. Pumps are rated by the following operational characteristics (Source: SWPA Handbook):
- Pressure Head: a measure of the pressure or force exerted by the fluid.
- Capacity: the rate of liquid flow that can be carried.
- Power input: the electrical input to the motor expressed in kilowatts (kW). A measure of the rate at which work is done.
- Power Factor: the ratio of the true power to the volt-amperes in an alternation current (ac) circuit.
- Motor Efficiency: a measure of how effectively the motor turns electrical energy into mechanical energy. It is the ratio of power input to power output.
- Motor Input Horsepower (EHp): the power input to the motor expressed in horsepower.
- Brake Horsepower (BHp): the power delivered to the pump shaft expressed in horsepower.
- Hydraulic Horsepower (WHp): the pump output or the liquid horsepower delivered by the pump.
- Total Efficiency: the ratio of the energy delivered by the pump to the energy supplied to the input side of the motor. Sometimes referred to as the ‘wire to water efficiency.’
- Pump Efficiency: the ratio of the energy delivered by the pump to the energy supplied to the pump shaft.
There are two basic types of pumps: centrifugal and positive displacement. In a centrifugal pump, water is moved by the force of a spinning impeller that essentially hurls water out and up. Displacement pumps use the reciprocating motion of a surface such as the fitted end of a piston or a pneumatic diaphragm to displace water from an inflow chamber. Building water supply systems will usually utilize a form of a centrifugal pump called a booster pump. This is especially true for building fire control systems which require continuous pressure and to raise pressures from the building’s water supply line. These pumps come in multiple configurations depending on the water’s end use. They have the advantage of being quick to install and can be inserted anywhere along the water pipeline. Simple to operate, they require less maintenance than displacement pumps while being easier to repair. One disadvantage is that they don’t operate as efficiently with high-viscosity liquids such as oils, but since these booster pumps are being used to pump low-viscosity water, this is not normally a concern to designers.
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Bell & Gossett Series 80 ITSC vertical in-line pumps were selected for the transfer from an electric heating system to hydronic distribution at New York’s Twin Parks housing development.
Inside a centrifugal pump, water enters the inlet of the impellor chamber via a suction port. Inside the chamber, curved impellor blades spin rapidly, imposing a centrifugal force on the water as it turns. The angle of and curvature of the blades themselves vary from pump to pump but the overall design is relatively simple. The impellor is housed within a body shell called the volute casing. The impellor array spins around an axis, which includes the suction port inlet. Water enters at the axis and rides along the curved surface of the impellor blade until it is flung against the inside of the pump’s casing. From there it flows along the casing walls in a gap between the ends of the impellor blade and the casing until it exits the pump via the discharge port at high velocity, carrying with it the force of the impellor motion in the form of increased pressure head.
Using the rating characteristics described above, booster pumps vary greatly in size, with flow rates ranging from as little as 5 gpm to 10,000 gpm. They typically apply a pressure head of 200 to 7,500 feet while usually operating in a power range between 1 to 5,000 horsepower. Booster pumps are often arranged in series with more than one impellor aligned along a single pipeline. This is done to increase operating head (by contrast, arranging pumps in parallel results in increased flow rates). They can be located anywhere along the water service pipeline to boost the pressure on potable water service, process water for industrial or commercial applications, fire protection, or for HVAC cooling water circulation. The applied pressures increase both the distance and height that water can be pumped and can increase the force of the spray at the water distribution point. However, care must be taken in the design of these booster systems to ensure that supply quantities are adequate and uninterrupted. This is necessary to prevent possible backflow and contamination from the building back into the water supply system pipeline.
Centrifugal booster pumps can be single-stage, with only one set of impellors, or multiple-stage with two or more in-line impellor assemblies. Single stage booster pumps are usually used in residential or single story commercial buildings. They are included to provide additional water pressure to those locations that are too far away from the source of the water supply system to receive adequate pressure. Multi-stage booster pumps are used at locations on top of a hill or other high elevation points where the extra height negates the natural pressure head in the water distribution system’s pipelines, or they are used in high-rise buildings and skyscrapers where the additional height to overcome is part of the building’s design. In addition to multi-stage pumps, several pumps can be used in-line if the situation calls for it.
Booster Pumps, Storage Tanks, and Building Water Distribution Design
But booster pumps are only one part of a building’s water distribution system. In addition to the actual pipelines carrying the water throughout the building’s structure, the system also relies on storage tanks. In addition to the simple rooftop storage tanks that subsequently feed water into the building’s water system via gravity, there are hydro-pneumatic pressure tanks that use air pressure to further increase the water supply pressure at the point of use. These tanks are located intermittently within the building structures according to supply needs and pressure requirements. They can drain via gravity or utilize dedicated booster pumps of their own to discharge water to their service lines.
Since they are subject to high pressure, these enclosed tanks are made from steel and fiberglass. The structural design of the tanks must be rated to their anticipated pressure loads along with an appropriate factor of safety. Each tank comes with pressure relief valves to prevent dangerous pressure buildups. In addition to the tank wall, fittings must also be built to withstand anticipated pressures. Tanks are typically armored with anti-corrosive coatings to prevent rust, corrosion, and contamination of the water supply. The size of the tank will vary in accordance with both total daily water use and peak daily water supply demand. However, they should not be designed too large since water can pool in the bottom of the tank for extended periods increasing the potential for contamination and stagnation.
Typically, a hydro-pneumatic tank is filled to one-third to one-half full. The water depth is controlled by a float level device that shuts off inflows once proper depth is achieved. Once full, interior pressure is maintained by an air compressor. As water leaves the tank, the water level drops. The expanded void space above the water surface also results in a fall in air pressure. The air compressor can then be turned on to increase pressure to maintain a constant head, and the float switch falls to the point where it triggers the water inflow back into the tank. This reduces the void space in the tank, raising air pressure again with any excess air pressure vented off via a pressure release valve.
Each combination of storage tank(s) and booster pump(s) within a building’s envelope is dedicated to a particular water pressure zone within a building. Larger buildings will be divided into multiple zones of pressure control depending on the building’s height and footprint area. Lower floors can be serviced directly by the incoming water distribution system’s service pipeline. Higher floors require more and more applied pressure head to provide water at sufficient pressure and flow rates. A standard practice is to group five or more stories together in a zone where water is fed at a consistent head either by gravity-down feed from a hydro-pneumatic storage tank or pressure-up feed from multi-stage booster pumps. Each zone’s pipe, tank, and pumps systems are kept isolated from the other to prevent cross-contamination or backflows from occurring.
What determines the arrangement and height of these building pressure zones? These zones are determined by the pipe pressure ratings. Simply put, the higher the building, the higher the pressures that the water supply pipelines will have to withstand. And so taller buildings require water service pipes with high-pressure ratings. The ability to withstand interior bursting pressures is a function of the material characteristics of the pipe and the pipe wall thickness. Serving as a design anchor point is the maximum allowable service pressure at a fixture, which by code is rated at 80 psi (equivalent to almost 185 feet of water column). Take, for example, a building design with a plumbing fixture needing 35 psi (81 feet of water column) at the top of a building pressure zone, and an 80 psi fixture at the bottom of the zone. This represents about 104 feet of water column difference between the pressure heads. So a building with floor elevations of 10 feet each could have a water pressure zone equivalent to 10 floors. However, this would require the strongest available pressure rating on the pipe which could increase the material costs of the piping considerably. So to reduce the pressure rating requirements on the service pipe lines, the designer may limit the size of the building pressure zones to only nine or eight floors. So the water supply system design would rely on the placement of hydro-pneumatic storage tanks every eight to 10 floors with associated booster pumps and appurtenances.
Major Booster Pump Suppliers
Booster pump and associated systems need controls. In addition to an extensive line of industrial and commercial pumps, AAON has an impressive product line of pump system controllers. It provides multiple control configurations, from a simple terminal block for a field-installed controller, to factory-installed controls which can be integrated into a building automation system. Their WattMaster Orion Control Systems controllers provide an efficient solution. The controllers allow users to take full advantage of AAON exclusive features without the need to design a unique control strategy for each application. The standalone AAON Jenesys Controller, powered by Niagara AX Framework, is an internet-based controller developed for network applications and is controlled (setpoint adjustment, scheduling, alarming, trending, logging, and diagnostics) by an internet browser in real time. This controller is IP addressable, residing in a TCP/IP network. The Micro Control Systems (MCS) Magnum Controller is installed on chiller equipment. It automatically cycles compressors to maintain the set point temperature of leaving water. Its large LCD display provides system information for scheduled service and maintenance. The MCS controller can communicate with building management systems.
Xylem is a leading global water technology company committed to developing innovative technology solutions to the world’s water challenges. The company’s products and services move, treat, analyze, monitor, and return water to the environment in public utility, industrial, residential, and commercial building services, as well as agricultural settings. Xylem does business under a number of market-leading product brands, including Bell & Gossett (B&G), A-C Fire Pump, Goulds Water Technology, and Lowara.
Xylem creates efficient systems and sustainable solutions, including energy-efficient pumps, boosters, drives, valves, controllers, water systems, and other solutions for clients who operate within the commercial, residential, agricultural, and industrial engineering sectors. Drawing on more than a century of experience in the water industry, Xylem has cultivated a strong culture of innovation and application expertise. In response to the Department of Energy’s Energy Conservation Standard for Pumps, the first-ever regulations for commercial and industrial pumps, Xylem brand Bell & Gossett introduced its e-Series line, the only pumps to meet the DOE’s efficiency requirements three years in advance of the 2020 compliance date.
As the world’s largest provider of water and wastewater treatment solutions, Xylem offers a range of wastewater pump systems, which are also necessary for large building applications. Products installed in these pump systems include submersible mixer pumps, hydro-ejectors, progressive cavity pumps, end-suction pumps, and submersible pumps (both wet and dry pit). Many of these pumps come standard with monitoring and control equipment, and can be used in a wide range of wastewater applications, including collection systems, low-pressure sewers, wastewater treatment plants, effluent pumping, and sludge management.
Xylem also designs and custom builds a wide range of state-of-the-art fire pumps and systems through its A-C Fire Pump brand. From small skid-mounted units to entire pump systems that are integrated into a building’s fire control pipe system, A-C Fire Pump is a leader in the fire protection industry. The company’s fire protection product line ranges from space-saving in-line pumps, to easily installed end-suction pumps, to vertical turbine pumps for static suction lift systems, to compact split case pumps and stainless steel multistage booster pumps.
In addition to being a leading provider of intelligent pump systems and related technologies, Xylem is focused on improving systems efficiency in order to realize dramatic energy and cost savings. An example of that commitment is B&G’s Efficiency Islands concept, a design approach that creates higher levels of efficiency over a broader range of operating conditions. According to a white paper published by B&G, “Efficiency Islands” are defined through total head vs. flow capacity performance curves for various ranges of horsepower and impellor diameter. There are many Efficiency Islands that make up the performance curve for a centrifugal pump. For the best operating performance, it is desired to have these Efficiency Islands be as wide (in terms of flow rate) and as deep (in terms of reduced impellor diameter) as possible.
B&G’s energy-efficient philosophy can be seen at work in the inside-out retrofit of New York’s Twin Parks Housing Project. An architecturally innovative urban renewal project from the 1970s, Twin Parks is now a leading example of energy efficiency, due in part to B&G’s Series 80 ITSC vertical in-line pumps, which replaced the housing development’s original electric heating system. ITSC stands for Integrated Technologic with Sensorless Control, a feature that combines sensorless technology with the energy savings of variable flow. In a case study about the project, Bob Demarco, vice president of operations at Platinum Energy Group, the contractor in charge of retrofitting the apartment buildings’ boiler rooms with new equipment, says Platinum chose the Series 80 because of its ease of installation.
LG Electronics USA’s applications show that building pumps are not just for potable water supply applications. Their extensive line of HVAC-related products also manages the circulation of water for large-scale industrial and commercial heating and cooling applications. This is best illustrated by an example of how their Variable Refrigerant Flow (VRF) technology provided a cost-effective solution for Euclid Chemical, based in Cleveland, OH.
Euclid Chemical’s main offices are in a two-story, 15,000-square-foot building that also contains laboratories where they develop products ranging from sealants to micro synthetic fibers. Until recently, the building relied upon an aging VAV system with terminal reheat to keep their offices comfortable and to maintain environmental conditions in the laboratories. Even when new, records showed the system had not performed as designed. This inadequate performance was compounded by cumulative effects of years of normal wear and tear plus questionable modifications. Analysis of the utility bills revealed that the building had an average annual energy use of 38 KwH per square foot—over twice the average consumption for offices in that geographic area and even more than most of Euclid’s manufacturing facilities. The system was made complicated by the unique challenge of quickly adapting to rapidly changing make-up air requirements as laboratory fume hoods started and stopped.
A solution was identified with VRF technology from Refrigeration Sales Corporation utilizing VRF technology from LG Electronics. Together they designed a system around LG Multi-V Heat Recovery systems. The bulky, 50-ton DX unit on the roof was replaced by a pair of small air-cooled outdoor units on the ground, and the VAV boxes inside the building were replaced with LG’s concealed high-static VRF indoor units. To account for the need for ventilation air and makeup air when the laboratory fume hoods were in use, a small makeup air unit with a water heating coil was added to provide ventilation air at a high-static pressure to the LG VRF indoor units. Since this was 100% outdoor air, the airflow could be adjusted to precisely meet the ventilation requirements as they changed. The LG Multi V is a heat recovery system, so it can heat the zones that need it while cooling others simultaneously which delivers precise temperature in all parts of the facility regardless of the weather and temperature. It was conservatively estimated the new system would cut their utility bills by 40%. What’s more, they could reuse the existing distribution and supply ductwork, reducing upfront installation costs, which further sold the financial team. And once installation was completed, the system performance exceeded expectations, with a 70% annual energy reduction compared to the average of the previous five years.