Hvac Connection Details

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Because it is not possible to show all of the details necessary for a proper installation of certain pieces of HVAC equipment on the floor plans or large-scale plans, it is necessary for the HVAC system designer to show this information in equipment connection details. These details will show all of the required ductwork and piping connections, as well as support requirements and miscellaneous appurtenances such as thermometers, pressure gauges, and flexible pipe connectors.

Also, it is common for details to be developed that describe miscellaneous items associated with the HVAC systems such as pipe hangers, roof curbs, and penetrations through the building envelope. Hence, we have provided some of most important details that every HVAC engineer and technician needs to know.

Contents

U-Tube Shell and Tube Heat Exchangers

U-tube shell and tube heat exchangers consist of a copper U-tube bundle mounted within a steel cylindrical shell. The cold fluid stream normally circulates through the tubes of the tube bundle, and the hot fluid stream normally circulates through the shell (around the tube bundle). Heat is transferred from the hot fluid to the cold fluid through the walls of the tubes. Shell and tube heat exchangers are commonly used to transfer heat from steam to water or brine. However, they can also be used to transfer heat from water to water, water to brine, or brine to water. Baffles are installed in the shell to direct water flow across the tubes if the heat exchanger is used to transfer heat from water to water, water to brine, or brine to water.

A minimum of two passes of the fluid through the tube bundle are required for U-tube shell and tube heat exchangers. For most HVAC applications, shell and tube heat exchangers are between 3 and 6 ft long and 6 and 12 in. in diameter, although larger heat exchangers are available. Figure below illustrates the piping connections to a steam-to-hot water shell and tube heat exchanger.

Plate and Frame Heat Exchangers

Connections for plate and frame heat exchangers are limited to the entering and leaving hot and cold fluid connections, which are normally an integral part of the (front) fixed head of the heat exchanger {although connections can also be provided in the (rear) movable head of the heat exchanger]. Depending upon the channel configuration of the heat exchanger plates, the entering and leaving connections for the hot and cold fluids can be located either on the same side of the heat exchanger fixed head or in a diagonal arrangement.

It is common for the hot and cold fluids to circulate through plate and frame heat exchangers in a counter-flow configuration; that is, the hot and cold fluids flow in opposite directions through the heat exchanger. This arrangement, in which the temperature gradient between the hot and cold fluids remains essentially constant, maximizes the heat transfer efficiency of the heat exchanger and also allows for a crossover temperature between the hot and cold fluids. Fig. below is a connection detail for a plate and frame heat exchanger.

Pumps

There are many types of pumps including end-suction, close-coupled, in-line, horizontal split-case, vertical split-case, and positive displacement pumps. The most common types of pumps used for hydronic systems are end-suction and in-line pumps, which are both centrifugal pumps.

End-suction pumps are attached to an integral steel base frame that is field-mounted to a concrete base. The concrete base can be a 4-in.-high housekeeping pad to which the pump base frame is mounted with spring isolators. However, the preferred mounting is a concrete inertia base to which the pump base frame is bolted. A concrete inertia base is a steel-framed concrete block that is approximately 6 in. high and 6 in. larger than the pump base on all sides which is supported off of the floor by spring isolators.

The concrete inertia base provides a rigid base to maintain alignment of the pump shaft and reduce the vibratory motion caused by the rotating pump motor. The pump suction pipe connection is parallel to the impeller shaft and the discharge pipe connection is perpendicular to the impeller shaft. Flexible pipe connectors are used on the suction and discharge pipe connections for end-suction pumps to isolate the vibration that is generated by the pump from the piping system. The suction and discharge connections for in-line pumps are in line with each other and are perpendicular to the pump/impeller shaft. Small in-line pumps are supported by the piping system. Large in-line pumps require pipe hangers to be installed near the suction and discharge connections. Very large in-line pumps will be supported from the building floor, usually on a 4-in.-high concrete housekeeping pad.

The piping connections required for pumps include shutoff valves on the pump suction and discharge, balancing valve on the pump discharge, check valve and flow meter on the pump discharge, and pressure gauges. As an option, a multipurpose valve, which performs the duties of a shutoff valve, balancing valve, and check valve, may be installed on the pump discharge. It is common for a suction diffuser, which is similar in size to that of a long radius 90° pipe elbow, to be used on the suction pipe connection for end-suction pumps. This allows the suction pipe to drop vertically into the suction diffuser. Otherwise, it is necessary to provide five pipe diameters of straight pipe upstream of the pump suction connection. If a suction diffuser or the necessary length of straight pipe upstream of the pump suction connection is not provided, undesirable turbulence in the fluid flow will occur at the pump suction connection, which will compromise the performance of the pump and may also damage the pump.

End-suction pumps range in size from 3 to 6 ft long and from 1 to 3 ft wide. The motor shaft is connected to the impeller shaft through a coupling.

In-line pumps are either vertical or horizontal, which describes the orientation of the motor/impeller shaft. The motor shaft is connected directly to the impeller shaft. In-line pumps range in size from 1 to more than 3 ft high (dimension from the impeller to the end of the motor) and 1 to 3 ft between the suction and discharge connections.

heating coil

Hot water coils require heating water supply and return piping connections, and steam coils require steam supply and condensate return piping connections.

ductless split-system unit

Connections to ductless split-system units include the refrigerant suction, liquid, and possibly hot gas piping between the indoor and outdoor units, condensate drain pipe connection to the drain pan, and electrical connections to the indoor and outdoor units. Because the indoor units are wall-mounted below the ceiling or recessed within the ceiling, it is common for there to be insufficient space for the pitch of the condensate drain piping. Therefore, a small condensate pump is usually installed adjacent to the indoor unit to receive condensate from the cooling coil drain pan and pump it to the point of discharge to the building storm water system. The connection of the condensate drain piping to the building storm water system should be made with a backwater valve in order to prevent the storm water surcharge that can occur during heavy rain from overflowing the condensate pump.

Ductless split-system units typically utilize 208/240V /1Φ electrical power. If a condensate pump is required, it should be specified to utilize 120V /1Φ power and be furnished with a cord and plug to serve as the disconnecting means. In this case, the electrical engineer would design a ground fault circuit interrupter (GFCI) receptacle near the condensate pump as its source of electrical power. Figure below illustrates the connection detail for a ductless split system unit, respectively.

Fan-Powered VAV Terminal Unit

Figure below illustrates the connections associated with a parallel fan-powered VAV terminal unit with a hot water heating coil. The connections far a series fan.-powered VAV terminal unit with a hot water heating coil would be similar, but the hot water heating coil would be mounted on the outlet of the terminal unit.

The heating water piping connections (depending upon the type of control valve) are similar to those shown in heating coils with 2 (or 3)-way valve. Also, a flexible duct connector is required. on the outlet connection of fan-powered terminal units to isolate the vibrations generated by the fan in the terminal unit from the downstream duct system.

HVAC Design  Sourcebook  W. Larsen Angel, P.E., LEED AP

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