What is HVAC Piping?
HVAC piping is a system of pipes used to deliver hot water, cool water, refrigerant, condensate, steam, and gas to and from the HVAC components employed in industrial, commercial, residential, and institutional buildings. This system is used to add or remove heat from the air inside the building, control humidity, filter the air and bring in fresh air.
Types and Materials for HVAC Piping
The cooling system consists of chilled water and condensate water. Chilled water systems use a closed loop to pump the water, with heat absorbed and passed off at three main points. These are the fan coil unit, the chiller, and the condensate water system. The heating system works by adding heat to the occupied space, and includes both the steam system and the hot water system. A boiler is used to produce the steam, and the heat is transferred into the hot water and carried to the occupied space. Steam traps and condensate pumps are used to collect the condensate and pump it back to the boiler. The hot water system is a closed-loop system and gets its heat from the heat exchanger, which is then pumped into the spaces within the buildings. These cooling and heating piping networks are collectively called HVAC piping systems.
Types of HVAC Piping Systems
Central Plant Equipment Room Piping: The central plant equipment room consists of the pipe networks connected to the rotating equipment and tanks. These systems are designed to supply process liquid to the other parts of the building. Heat exchangers, pumps and other equipment are connected to the pump room to ensure effective functioning of the system.
Delivery Piping: The delivery piping system is used to transport the process liquid from the central plant equipment room to the other parts of the building. The delivery piping is designed to ensure efficient and safe delivery of the liquid to its intended destination. Different types of pipes are used in this system such as steel, copper, and plastic pipes. These are designed to withstand the high-pressure and temperature levels required by the process liquid.
HVAC Piping Materials
HVAC Piping materials are an important factor in determining the effectiveness of the piping. Copper and steel are the two most commonly used metals for HVAC piping.
Copper Piping: Copper is used primarily for smaller piping, transporting water in AC units with a maximum commercial size of 12”. Copper is expensive and is thus used mostly for piping that is 3” and smaller.
Steel Piping: Steel is much more cost-effective and is used for larger sizes. It is able to withstand higher pressure than copper and is ideal for both hot and cold water. Sch 40 and Sch 80 pipes are often used in HVAC applications.
ASTM Piping: For larger piping applications, ASTM A53 or A135 (light wall black steel pipe) is used for chilled and heating water services 8” and above. ASTM A120 and A53 (black steel pipe Sch. 40) is used for miscellaneous drains and overflows, emergency generator exhaust, safety and relief valve discharge, chemical treatments, and high- and low-pressure steam. ASTM 120 and A53 Sch. 80 (black steel pipe) is used for pumped and gravity steam condensate return. ASTM A120 Sch. 40 (galvanized steel pipe) is used for miscellaneous indirect wastewater pipes.
Copper Piping: ASTM B88 (copper pipe) is used for industrial cold water (above grade-type L) for piping 4” and smaller, refrigerant piping (type L, hand-drawn) below 6”, and chilled and heating water (type L and hand-drawn) below 3”.
Protection Against Corrosion: For underground pipes, cathodic protection is used to prevent corrosion from dirt. This is done by coating it in a thin layer of some other metal such as zinc to absorb the corrosion. The flanges used are per ANSI B16.1. Cast iron or steel is used for screwed pipe and forged steel welding necks are used for welded line sizes.
Plastic Piping: Plastic piping is much cheaper than copper and steel and is often used for HVAC applications. It is thinner and weaker and won’t be able to withstand much pressure. It does not corrode, making it suitable for underground uses. PVC and CPVC are the two types of plastic piping commonly used. They will not be able to withstand a wide range of temperatures as metal.
HVAC Piping Insulation
HVAC piping systems are usually insulated to minimize temperature loss or gain and protect against corrosion. The most common type of insulation used is closed-cell elastomeric foam pipe insulation, which has a closed-cell structure and built-in vapor barrier, and can withstand temperatures ranging from -297°F to +220°F. Other types of insulation include mineral fiber insulation, preformed pipe insulation, blanket insulation, fire-resistant adhesive, vapor retarder mastics, mineral fiber insulating cement, prefabricated thermal insulating fitting covers, and elastomeric cellular thermal insulations. Buried HVAC piping parts are wrapped according to AWWA C209 and C214 standards.
Types of HVAC Piping Insulation
Closed-Cell Elastomeric Foam Pipe Insulation: This type of insulation is the most commonly used due to its closed-cell structure and built-in vapor barrier. It can withstand temperatures ranging from -297°F to +220°F.
Other Insulation Options: Mineral fiber insulation, preformed pipe insulation, blanket insulation, fire-resistant adhesive, vapor retarder mastics, mineral fiber insulating cement, prefabricated thermal insulating fitting covers and elastomeric cellular thermal insulations are also available.
Buried HVAC Piping Insulation: Buried HVAC piping parts must be wrapped according to AWWA C209 and C214 standards.
Analysis of HVAC Piping Systems
A comprehensive analysis of a HVAC piping system must be conducted to ensure it meets the necessary code requirements and can withstand the different loading conditions. This analysis should include verifying the design temperature, ambient temperature, operating temperature, design pressure, and hydro test pressure. Furthermore, the materials used must be selected based on the process parameters to ensure it meets safety requirements. Expansion compensators may also be required to accommodate the expansion and contraction of the HVAC piping network. Generally, ASME B31.9, B31.3, and B31.4 are used for utility service piping, underground piping, and other applications, respectively.
Loads and Displacements on HVAC Piping Supports
The displacement and loads on the supports of a HVAC piping system must also be verified. Plastic piping may have more displacement due to its elastic properties, so it is important to consider this when analysing the system. Quality assurance must also be taken into account to ensure that the piping materials and installation meet the local building codes and service utility requirements.
Support Spacing of HVAC Piping System
Horizontal HVAC piping system for support span is given below
| Pipe Size | Maximum Support Spacing | Common Hanger Diameter if supported using Rigid hangers |
|---|---|---|
| 1/2 to 1-1/4 inches (12.7 to 31.75 mm) | 6 feet 6 inches (2 m) | 3/8 inch (9.5 mm) |
| 1-1/2 to 2 inches (38.1 to 50.8 mm) | 10 feet (3 m) | 3/8 inch (9.5 mm) |
| 2-1/2 to 3 inches (63.5 to 76.2 mm) | 10 feet (3 m) | 1/2 inch (12.7 mm) |
| 4 to 6 inches (101.6 to 152.4 mm) | 10 feet (3 m) | 5/8 inch (15.9 mm) |
| 8 to 12 inches (203.2 to 304.8 mm) | 14 feet (4.25 m) | 7/8 inch (22.2 mm) |
| 14 inch (355.6 mm) and over | 20 feet (6 m) | 1 inch (25 mm) |
| PVC (All sizes) | 6 feet (1.8 m) | 3/8 inch (9.5 mm) |
| C.I. Bell and Spigot (or No-Hub) | 5 feet (1.5 m) at joints | 3/8 inch (9.5 mm) |
Supporting Horizontal Cast Iron HVAC Pipes
For horizontal cast iron HVAC pipes, they should be hung with hangers or supports no more than 5 feet (1.5 m) apart. This is to ensure that the pipes are adequately supported and can bear the weight to which they are subjected.
Supporting Vertical Cast Iron HVAC Pipes
When it comes to vertical cast iron HVAC pipes, they should be supported at each hub, as well as on each floor. This is to ensure that the pipes are properly secured and can properly handle the weight of the pipes. Additionally, it helps to reduce any potential vibrations that could cause damage to the pipes.
Joining HVAC Piping
When installing an HVAC piping system, there are certain guidelines that should be followed in order to ensure proper joining of the pipes.
Using Soldered Joints for Copper HVAC Piping: Soldering is the preferred method for joining copper HVAC piping. This method should be used in accordance with the manufacturer’s instructions, as well as any relevant codes and standards.
Utilizing Screwed, Flanged, or Welded Joints for Steel HVAC Piping: Steel HVAC piping requires a different type of joining method, such as screwing, flanging, or welding. All of these methods should be used in accordance with the manufacturer’s instructions and applicable codes and standards.
HVAC Piping Frequently Asked Questions
What Types of Pipes Are Used for HVAC Systems?
When it comes to HVAC piping, Steel, Copper, and PVC are the most commonly used materials. Copper is typically used for pipes with a diameter of 3 inches or less. PEX tubing is increasingly replacing copper in cold and hot water applications.
What is a Two-Pipe HVAC System?
A two-pipe HVAC system is a cost-effective option that uses the same piping system alternately for chilled water cooling and hot water heating.
What Type of Pipe is Used for Chilled Water?
Steel pipe is the most commonly used material for chilled water piping systems.
What Type of Copper Pipe is Used for HVAC?
Type L Copper Pipe is the most common type of copper pipe used in HVAC systems. It is available in rigid and flexible forms.