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ENGINEERING HANDBOOK FOR THE DESIGNER OF HYDRO-PNEUMATIC APPLICATIONS IN ENGINEERED MECHANICAL SYSTEMS… This design handbook concerns the design, selection and application of hydro-pneumatic components in commercial, industrial, institutional and high-rise residential mechanical piping systems. Hydro-pneumatics—Can best be defined as the use of a gas, (usually air), in a liquid- filled piping system to control operating pressure, liquid expansion, and water hammer during system operation in applications for space heating and cooling; water heating (potable and process); and water supply applications (well systems and pressure booster systems). Section A, beginning on page A-1, will deal with the fundamentals of hydro-pneumatics in liquid heating and cooling systems. Section B, beginning on page B1, will cover sizing and design requirements, sizing procedures, installation and application variations of EXTROL hydro-pneumatic (expansion) tanks for hot water and chilled water hydronic systems. Section C, beginning on page C-1, will deal with air removal procedures in large hot water heating and cooling systems. The contents of each section are provided to aid the professional designer, specifier and estimator of engineered mechanical systems in selecting and applying hydro-pneumatic products as originally designed and produced by AMTROL Inc., to arrive at the most efficient and dependable system operation possible. In the future, the contents of this binder will be up-dated as new breakthroughs in the ever-changing mechanical systems field are made. The Reference Section contains appropriate data tables as referenced throughout the text. ©AMTROL, Inc. 1977, Reprinted October 2011 MC 4402P i Section A Hydro-pneumatics in hot water and chilled water systems Chapter One PRESSURIZATION OF HOT WATER HEATING AND CHILLED WATER SYSTEMS The basic function of hydro-pneumatics in a closed piping system transmitting water or a similar liquid for heat transfer or cooling applications is over-all sys- tems pressurization, and the maintenance of minimum-maximum pressures during all operating temperatures of the system. CLOSED SYSTEM VS. OPEN SYSTEM CLOSED SYSTEM ADVANTAGES: The advantages of a closed piping system in hot water heating and chilled water cooling as compared to an open system are many: 1. Minimum make-up water required. 1. Little, if any, make-up water is required to maintain a filled system as little or none is lost through evaporation or steaming as in an open system where the water content of the system is open, at some point, to the atmosphere. 2. No accumulation of oxygen from constant make-up water. 2. With very little fresh water added, there will be no meaningful accumulation of oxygen and other entrained corrosive agents in the system once it is initially purged. This extends the life expectancy of the system indefinitely. In an open system, on the other hand, entrained air and other corrosive agents accumulate rapidly through the constant entrance of make-up water. 3. Operating temperatures above 212°F. 3. In a closed system the entire system is pressurized so that operating temperatures can be higher than 212°F without causing flashing or boiling in the system. This allows reduced sizing of piping, terminal units and heat generators. In an open system, maximum operating temperatures must be kept below 4. Operating economy and conservation of water and energy. 4. In a closed heating system, there is very little or no loss of water or heat as system water remains in the piping. During the evaporative process in a system open to the atmosphere, there is a constant loss of water and BTUs. Constantly entering cool make-up water requires frequent burning of fuel to maintain system temperatures. 5. Positive pressure assures constant venting. 5. In a closed system, pressurization can maintain a positive pressure in the system at all times so that excess air can be eliminated through simple automatic air venting devices. In systems open to the atmosphere, pressures in a negative range can draw air into the system creating corrosive and circulation problems. A1-1 ©AMTROL, Inc. 1977, Reprinted October 2011 AIR ELIMINATION Air Elimination…Not Air Control ne tic c ion per nent. Air in P uma ush ma It has been thought for many years, that for ideal pressurization of make-up water can be eliminated. a closed hot water heating or chilled water system, a perfectly and hermetically sealed piping system is mandatory for ideal air-free performance. While this is in theory ideal and should be the objective in any designer’s mind, it is also acknowledged that such a completely pressure-tight, leak-proof state is understandably difficult to insure. Especially in a large, complicated engineered mechanical system such as found in the modern high-rise building. Therefore, facing the reality that the ideal may not be reached, the designer of a closed piping system should incorporate into the basic system a provision for continuous and automatic elimination of excess air that will surely find its way into the system through AIR CONTROL fresh water which must be added to the system. ne tic c ion con t nt P uma ush s a ly While the traditional approach to air, as the pressurizing agent in b orbed in te ter nd a s sys m wa a the system, has been one of controlling air (i.e., collecting and re- circulated throughout system. directing it to the compression tank), this manual will discuss the Must be collected and directed use of the EXTROL concept of permanently separating the air used back to tank to maintain for pressurizing the system from system water. Therefore, any pressurization. other excess air may be collected and eliminated from the system as soon as it enters. This subject of air removal versus air control will be fully covered in Section C. The Function of the Hydro-Pneumatic Tank Adequate 5 PSIG The primary device in pressurizing and maintaining pressure Positive control in a closed system is the hydro-pneumatic tank, also Pressure known, traditionally, as the expansion or compression tank. Its function in the pressurization process is as follows: 1. Through the use of a pneumatic cushion (air), it maintains 100′ = 43 PSIG t tic positive minimum pressure throughout the system when it is 48 PSIG— S a Pressure initially filled. MINIMUM OPERATING 2. During temperature rises, it provides an additional space in the PRESSURE system for the expanded volume of water that results. This is IN TANK accomplished as the pneumatic cushion is compressed as system pressure increases, creating additional space for the increased volume of water. As the system temperature drops, the compressed pneumatic cushion forces water back into the system, maintaining a positive pressure on the system during all temperatures in the system’s operating range. 1. Pneumatic cushion eliminates 3. Properly sized, the hydro-pneumatic tank will maintain need of charge water during maximum system pressures within the working pressure limitations system fill with a minimum of the system equipment and components. operating pressure on system. 4. By maintaining a positive pressure on the system throughout all the operating temperature range, the hydro-pneumatic tank enables the designer to constantly vent excess air through the use 2. Accepts expanded water as of automatically operating float type air vents. system temperature rises. Li it i te 70 PSIG MAXIMUM 3 m s max mum sys m OPERATING operating pressure to within safety PRESSURE setting. 4. Assures a positive pressure at all times to keep pressure above “flash” point of water and assures constant venting. A1-2 ©AMTROL, Inc. 1977, Reprinted October 2011 PRESSURIZATION OF WATER HEATING AND CHILLED WATER SYSTEMS The selection of the hydro-pneumatic tank will establish a base for determining the over-all pressurization of the systems. Before Adequate 5 PSIG discussing the selection and sizing procedure, it would be Positive advisable to evaluate the various pressure and temperature factors Pressure and their relation to pressure control. A. Minimum Operating Pressure at the Tank Plain Steel 100 This is the pressure required, at the tank location, to keep the Tank System ′ = 43 PSIG Static system completely filled, plus an additional pressure to insure Pressure positive pressure at the top of the system. In heating, this positive pressure must be above the flash point of the water at its maximum operating temperature. In determining the minimum operating pressure, two factors must be considered: 48 PSIG 1. Static Pressure at the Tank Location – This is the pressure 48 PSIG caused by the physical weight of the water above the tank. Since Minimum Operating 2.31 feet of water exerts a pressure of 1 pound per square inch Pressure gauge (psig) the height of the system above the hydro-pneumatic at Tank tank divided by 2.31 will give the static pressure at that point. This is the pressure required to fill the system to the top. The height of the system above the plain steel hydro-pneumatic tank will be the pressure to which the system water will compress the air cushion in the tank when the system is filled. In a high-rise system, for example, with the tank located in the basement of a building and 100 feet of water above it, the static Fig. A-1 pressure at the tank would be approximately 43 psig. 2. Adequate Positive Pressure – To the static pressure above, it is necessary to add an additional positive pressure at the top of the piping system when it is initially filled. This insures positive 43 PSIG + 5 PSIG = 48 PSIG pressure at all times so that air can be constantly vented and Static Adequate Minimum negative pressures can not occur to draw air into the system Pressure Positive Operating through vents.

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