1 CHAPTER 8. PIPING EQUIPMENT AND SYSTEMS 8.1 Piping System and Components 8.2 Piping 8.3 Pumps 8.4 Valves 8.5 Pipe Fittings and Accessories
2 8.1 Piping Systems and Components Piping systems are classified as follows: 1) Service provided: Heating, cooling, oil supply, condensate return, etc. 2) Medium conveyed: Steam, hot water, chilled water, refrigerant, oil, gas, condensate, chemicals, etc. 3) Pressure class: Low-, medium-, or high-pressure classes. 4) Temperature class: Low-, medium-, or high-temperature classes. 5) Piping arrangement: One-pipe or two-pipe system, direct or reverse return, series or parallel flow, etc. 6) Hydraulics: Gravity or forced flow, open or closed flow. 7) Piping materials: Steel, copper, plastic, nonmetallic, etc.
3 8.1.1 Forced or Gravity Flow Forced system: Most piping systems use pumps or compressors to main the flow of the fluid. Gravity system: Depends on gravity to maintain the flow of the fluid. Forced flow of refrigerant: vapor phase: compressor liquid phase: pump
4 8.1.2 Open or Closed System In an open system, the fluid surface is exposed to the atmosphere. The flow may be either by gravity or by pumping. In a closed system, fluid is not in contact with the atmosphere. The flow must be by pumping. Most HVAC piping systems are closed systems.
5 8.1.3 Series or Parallel Pumping Series pumping: For equal-sized pumps, a series arrangement doubles the head (m). Parallel pumping: For equal-sized pumps, a parallel arrangement doubles the flow (L/m)
6 8.1.4 Direct-return or Reverse-return System In a direct-return piping arrangement, equipment closest to the pump has the least pressure loss, and thus may have more water flow. In a reverse-return system, the water flows through multiple units of HVAC equipment at the same rate.
7 8.1.5 Piping Arrangement for Heating by Boiler (Mechanical and Electrical Equipment for Buildings, 10 th Ed., p.339)
8 8.1.6 Basic HVAC Piping Systems Pipes: to transport fluids Pumps: to provide power for transporting fluids through pipes Valves: to control the fluid flows Pipe fittings: elbows, tees, flanges, couplings, unions, etc. Accessories: strainers and temperature-, pressure-, and flow-gauges.
9 8.2 Piping Materials for Pipes General purpose piping for HVAC systems are constructed of plain (black) steel, galvanized steel, copper, or cast iron. Special applications requiring corrosion resistance may require nonmetallic materials, such as fiberglass, plastic, or glass, or more expensive metallic materials, such as stainless steel or aluminum. Fiberglass and plastic are require extra design attention to prevent damage from water hammer. Thermal expansion needs to be considered carefully; plastics expand at a much higher rate than metals. Plastic piping is made of: PVC polyvinyl chloride CPVC chlorinated polyvinyl chloride PB polybutylene PE polyethylene PP polypropylene
10 1) Black Steel Pipes Uncoated steel pipe, called black because of the dark-colored iron-oxide scale formed on its surface These pipes are usually used for low-pressure hot-water heating pipes.
11 2) Galvanized Steel Pipes Galvanized steel pipe is a steel pipe that has been coated with zinc. This coating protects the steel from corrosion. It is most commonly used for outdoor construction like fences and handrails, or for some interior plumbing. It is also sometimes called galvanized iron pipe.
12 3) Copper Pipes (Tubes) Copper pipe is used both for plumbing and air conditioning. Pipe for residential plumbing, or plumbing tube, is sold in nominal sizes which are 1/8 inch less than the actual outside diameter. There are four types (K, L, M, and DWV): - K: tubes with the thickest walls, typically used for underground burial. - L: used for most purposes. - M: tubes with thinner walls than L types, used for drainage and other low-pressure applications. -DWV: tubes with the thinnest walls used for drain, waste and vent. Temper: Types K and L are available in two tempers: drawn temper (often called hard), and anne aled temper (often called soft).
13 Drawing Drawing simply involves pulling the hollow tube through a series of hardened steel dies to reduce its diameter. Annealing Tube that is to be sold in the soft condition, generally as coils, is next passed through a continuous annealing furnace operating at 700 C.
15 4) PVC Pipes A polyvinyl chloride (PVC) pipe is made from a plastic and vinyl combination material. The pipes are durable, hard to damage, and long lasting. A PVC pipe does not rust, rot, or wear over time. For that reason, PVC piping is most commonly used in water systems, underground wiring, and sewer lines at the lowest cost. It is joined by solvent cementing, threading, or flanging. Gasketed push-on joints are also used for larger sizes.
16 5) CPVC Pipes Chlorinated polyvinyl chloride has the same properties as PVC but can withstand a higher temperature (typically 40 C to 50 C ) before losing strength. This is a popular material for water piping systems in residential as well as commercial buildings. It is joined by the same methods as PVC.
17 6) PB Pipes Polybutylene, developed in 1970 s, is a gray plastic used for both hot and cold plumbing water piping. A PB pipe is light and flexible and can be used up to 99 C. It is joined by heat fusion or mechanical means, can be bent to a 10 diameter radius, and is provided in coils. However, in the 1980 s, buildings with PB piping started reporting leaks. And when PB pipes were replaced, it was noticed that the interior walls of the pipes and fittings were breaking down and flaking apart. Polybutylene water pipes are no longer accepted by United States or Canadian building codes and have been the subject of class action lawsuits in both countries.
18 7) PE Pipes Low-density polyethylene (LDPE) is a flexible light tubing with good low-temperature properties. It is used in the food and beverage industry and for instrument tubing. It is joined by mechanical means such as compression fittings or push-on connectors and clamps. High-density polyethylene (HDPE) is a tough, weather-resistant material used for large pipelines in the gas industry. Fabricated fittings are available. It is joined by heat fusion for large sizes; flare, compression, or insert fittings can be used on small sizes.
19 7) PP Pipes Polypropylene is a light plastic used for pressure applications and also for chemical waste lines, because it is resistant to corrosion towards alkaline and acidic solutions. PP pipes can withstand higher temperature up to 90 C. A broad variety of drainage fittings are available. For pressure uses, regular fittings are made. It is joined by heat fusion.
21 8.2.2 Methods for Joining Pipes Joints can be soldered, brazed, welded, screwed, flanged, solvent-welded, or mechanically coupled.
27 8.3 Pumps Pumps are used to convey fluid from one place to another by mechanical means. They can be classified into two main groups, namely, centrifugal and positive displacement pumps Centrifugal Pumps Centrifugal pumps make use of centrifugal force to work. The liquid to be pumped is usually water. The construction of the housing is such that water is piped in at the centre of the impeller. The impeller is then rotated at a high speed so that the water is thrown outwards with high velocity. The housing of the impeller is usually constructed in the shape of a volute such that the volume is gradually expanded until the placed the water is led out as the discharge. The gradual expansion of the volume has the effect of converting the velocity of the water into pressure
30 Multistage Centrifugal Pumps A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. If a higher pressure at the outlet is needed, the impellers are connected in series on the same shaft. If a higher flow output is needed, the impellers are connected in parallel on different shafts.
31 8.3.2 Positive Displacement Pumps Positive displacement pumps make use of a mechanical object to displace the liquid. The liquid to be pumped can be water, oil, or other thick liquid. The mechanical object can move in a reciprocating manner or a rotary manner. Examples of the mechanical object are: pistons, gears, screws, lobe, vanes. One characteristic of these pumps is the fact that the pressure can build up in time if it is not released. Usually a pressure relief valve is fitted at the discharge side of the pump to prevent over pressure.
32 8.3.3 Distributed Pumping In a variable-speed distributed pumping arrangement, constant flow pump(s) re-circulate the chiller or boiler source in a primary source loop, and a variable-speed zone or building pump draws flow from the source loop and distributes to the zone load terminals. The speed of the zone or building distribution pump is determined by a controller measuring zone differential pressure across supply-return mains or across selected critical zones. Two-way control valves in the load terminal return branch vary the flow required in the load.
33 8.4 Valves Functions of Valves Shutoff valves are installed to isolate components and portions of systems. Drain valves are installed at equipment and at the low points of piping system. Hose and fittings are normally used, and fluid is transferred to the nearest floor drain. Balance valves are installed to adjust the flow through the system in proper amounts to serve loads. They can also be used as shutoff valves. Control valves are installed to modulate the flow of fluids through heat transfer devices in response to fluctuating loads. Unlike shutoff and balance valves, control valves are in continuous operation. -A two-way control valve is installed in series with the load device and simply throttles the flow in response to the load. This control method results in a variation of flow. -A three-way control valve is arranged to force fluid through the load device or to bypass fluid around the load device, resulting in a constant system flow.
34 Back-pressure regulators can be used to avoid unacceptably high system pressure at light load conditions. Check valves allow flow to occur in only one direction. They are installed in multiple pump applications to prevent backflow through pumps that are not running. Pressure-reducing valves (PRVs) are installed to reduce the pressure of supply water or steam.
35 8.4.2 Types of Valves 1) Gate Valves Gate valves are used to isolate flow. These valves have a low resistance to flow when they are wide open. These valves are used for shutoff duty and are not intended to regulate flow.
36 2) Globe Valves Globe valves are used to isolate (on/off) as well as control flow rate (L/s). These valves have a high resistance to flow even when wide open.
37 3) Ball and Butterfly Valves These valves are used to control flow rate. They can also be used for isolating flows.
38 4) Check Valves
39 5) Pressure Reducing Valve (PRV)
40 8.5 Pipe Fittings and Accessories Many fittings and accessories are required to make a complete operational piping system. Common fittings and accessories: - Pipe fittings: elbows, tees, flanges, couplings, unions, etc. - Strainers: contain a perforated basket to entrain objects large enough to cause damage on sensitive components that have moving parts. - Pressure and temperature taps: installed to allow the insertion of gauges to check the performance of systems and components.
44 Air management: - A primary concern in hydronic system design is dissolved air in water. - The solubility of air in water decreases as the water temperature rises. - Air migrates to high points of the piping system and may curtail the water flow. - Air in heat transfer equipment also reduce the effective heat transmission. - Therefore, un-dissolved air must be eliminated from the system.