Pipe and valve selection for a cooling system

Compiled by Eamonn Ryan

Each component of valves, pipes and controls throughout a cooling system is critical to the overall efficiency and effectiveness.

Danfoss ABQM FCU Valve and acuuator installed in very tight space

Images supplied by Automated Control Solutions

When designing a cooling system, it is crucial to choose the right pipes and valves. It’s important to understand the options available and the possible outcomes associated with each selection. Many factors can impact the effectiveness, longevity and quality of the overall cooling system, and each of these factors should be examined when choosing the best pipes and valves for the application. In most cases, valves, piping and sensors are all key factors to a cooling system’s effectiveness and overall quality.

PRESSURE INDEPENDENT CONTROL VALVES

Automated Control Solutions (ACS) supplies several brands of control and balancing valves. Today, ACS primarily distributes Danfoss, iSMA Controlli, Genebre and Honeywell valves and Actuators, particularly for chilled water application. ACS services HVAC system integrators and mechanical contractors with high end quality international products.

Danfoss ABQM DN150 installed at a local Data Center

Adrian Hofmann, technical sales and support at ACS, says: “when it comes to the big tenders for large buildings and shopping malls, engineers like good quality valves and Danfoss and iSMA Controlli valves fit the bill nicely. There are two different sets of valves we do from Danfoss and iSMA Controlli: conventional two- and three-way control valves with manual balancing. This is the traditional way that people still use valves – up to about 150mm in two-way, and in three-way up to 300mm for chiller plant managing. We also do Danfoss’ AB-QM 4.0 range, which  is their Pressure Independent Control Valve (PICV) solution from 10mm up to 250mm, which are massive pressure independent control valves combined with automatic balancing valves. In particular, data centres like those valves because they require less commissioning and have far better control with up to 100% valve authority. PICV are combo two-way control valves with built-in automatic balancing valves which also save space on the valve arrangement, as there is now only one valve installed instead of two – this makes for a very neat installation.”

iSMA Controlli valves and actuators are an alternative to Danfoss, they have some highly specialised stainless-steel options with actuators suitable for outdoor installations with IP65 enclosures – unique products with competitive pricing. Conventional valves have been around a long time and Hofmann explains that one can either have on-off control or modulating control. “Modulating control is not new and gives superior control of the water flow.You’d have a controller like an ‘iSMA AAC20’ on an AHU unit giving a 0-to-10-volt signal to the actuator, which would be open or closed or anywhere in between the whole time, depending on the demand through the building,” says Hofman.

In the past, there were constant flow systems with three- way valves. There could be a set of pumps running full blast all day long regardless of the load, with the only thing changing being that the valve opens and closes, and water either goes through the coil or bypasses back to the chiller – a highly energy- inefficient system. “Now, with the design of the PICV, it’s a control valve and an automatic balancing valve all in one piece. There is no running up and down for weeks balancing the system – the valves are pre-set on installation, and they will take care of the There’s no bypass at the coils, which means variable speed drives (VSD) can now control the pumps to maximum efficiency, in the morning and evening, when the load is low, the VSDs run slowly, and entire plant runs more energy efficiently. As a result, those PICVs have grown in popularity – even though they’re more expensive than conventional valves, they provide a good return on investment on energy saving alone, never mind the savings on installation and commissioning,” says Hofmann.

BALANCING THE SYSTEM

He says the PICV is pre-set according to the flow requirement during installation, the valve taking care of the rest. The manual balancing valve can only be set once the water is pumping through the whole system at full load. Only at that point can the commissioning engineers start adjusting each valve, whether it be for fan coil units, AHUs, the branches or the risers – on big systems there are typically hundreds of these valves. What happens is, as one starts throttling these manual balancing valves to let the required amount of flow through, pressure starts increasing in the rest of the system, with the result the commissioning engineers must return to the previous valves to balance them again, this could take approximately two to three attempts ‘per   valve’ to   balance the system.

“PICVs always let just the required amount through the coil, regardless of changing system pressures, so the pump is running at the right speed, and the whole system is more efficient – for a power saving for the end user. They’ll pay more from the start but get their money back from power savings, normally well within two to three years. Unfortunately, it is often about the capex rather than opex. The mechanical engineer designs the system according to the client’s budget and it is the price of the system that ultimately determines which solution they go for.

“However, when a building is aiming for green star rating certification from the Green Building Council SA (GBCSA) they will certainly budget for PICVs in order to get the energy savings and the points. As green buildings are being pushed quite extensively, we have been seeing an increasing adoption rate over the past 10 years. However, there are still plenty developers who are not worried about their client’s energy usage because of the upfront cost,” adds Hofmann. He notes that Danfoss PICVs can be retrofitted to existing two-way systems. “It is messy work – but there is no question that it will pay for itself in a very short time.”

WHEN COOLING SYSTEMS ARE EXPOSED TO THE ATMOSPHERE

Cooling towers are often open to the atmosphere, which exposes them to outside elements. To combat this issue, it’s typically required to treat the water with a series of decontaminants that will aid in the slowing of corrosion and erosion caused by the chemicals and foreign particles in the water that is used to cool the system. Closed systems may be used for smaller cooling applications.

Choosing the best piping for a cooling system is a crucial part of the assembly process. There are five types of piping that can be used for a cooling system: tubing, iron, steel, stainless steel or exotic alloys, and plastic. The size and type of piping that should be used in the system is determined by factors such as the desired velocity through the system and compatibility with the fluid and chemicals that need to be introduced into the system to ensure efficiency. The size of the piping is important but can easily be determined by how much water needs to flow through the system. Higher grades of piping material come with a higher cost but will help with longevity and reliability. The compatibility of the piping system is important because water will be running through it at a near-constant flow rate. As the flow rate of water increases, a more chemically resistant pipe material is required to better hold up to corrosion.

If there is corrosion within the piping system, there can be a number of issues, including leaks within the piping system where water can seep through, and corrosion builds up in the pipe. Corrosion will inevitably reduce the flow area of the water. This corrosion issue is more predominant in small systems. The diameter of the pipe is a crucial factor to consider in the design of a cooling system.

The size of the pipe must be calculated correctly to ensure that it fits with the overall system, with the calculations of the pipe diameter accurate so that the velocity of the system is optimised and efficient. If the velocity is minimised throughout the system, then the water will be able to freely run and cool areas. Additionally, there will be less corrosion if the velocity is kept to a minimum.

The introduction of chemicals in the water is the last element to consider when looking at piping. In an open-atmosphere system, chemicals are typically introduced to control the pH level of the water. If chemicals are not introduced and the pH levels are not monitored, corrosion is likely in the piping system, causing a slow flow of water. In closed systems, there tend to be fewer minerals in the water. Consequently, closed systems can use aggressive fluids such as de-ionised water, requiring the use of plastic piping or stainless steels rather than iron or steel.

CHOOSING THE RIGHT VALVE TYPE FOR A COOLING SYSTEM

When it comes to cooling systems, the valves that are selected are typically going to be flow control valves and shutoff or bypass isolation valves. There are a number of points to consider before picking the valve for the cooling system:

• The flow capacity, for which it is important to remember in valve selection the pipe size.
• What flow capacity is needed for the cooling system?
• What size piping will be used?

The valve pressure/temperature rating must be within the system design parameters. The initial factor to be considered is the maximum pressure that the cooling system will have to hold, to determine the valve rating. Regarding the capacity of the system, consideration should be given to choosing whether a small-diameter pipe (globe control valve); mid-diameter pipe (segmented ball valve); or large-diameter pipe (high performance butterfly valve).

Different types of isolation valves also are considered based on pressure and related capacity:

• Small-diameter pipe: two- or three-piece ball valve
• Mid-diameter pipe: three-piece or flanged ball valve
• Large-diameter pipe: butterfly valve

The capacity of the overall cooling system is something that should be considered – the smaller the system size, the more accurate it will likely need to be. The cooling system in a CPU liquid cooler is one that should be accurate as there is a finite amount of space the water works with to cool the variables along the piping system.

This is not to say that the accuracy of the valve is not important in large systems. Rather, it is simply to understand when selecting a valve the factors that make up the valve’s accuracy. The factors that make one valve more accurate than another include construction of the valve, complexity of internal components and higher engineered designs. The preciseness of the valve is therefore key: it could be a needless expense to buy an extremely precise and more expensive control valve when a less precise one could have done the job just as well. Consequently, it is important to determine the margin of error that a system can endure while  still being efficient.

Finally, it is important to narrow down valve selection by taking a look at the heat transfer fluids – such as water – that will be involved in the cooling process system:

• What is the source of the fluid?
• What is the target water temperature?
• To what degree does the system need to be cooled down?
• What is the temperature of the water when it is introduced into the system?
• Is the water clean?
• Is the water going to be treated before it reaches the valve?

These questions will also determine the material of construction selected for the cooling system and valves, based on the strength needed in the system (pressure and temperature rating); the internal and external environment of the system (open or closed); and the resistance to corrosion or erosion of the fluid being used to cool the system.

THE CRUCIAL ROLE OF PIPES AND VALVES

Pipes are used to transport refrigerant, water and air between the various components of the system, while valves are used to regulate the flow of these fluids. Their proper functioning is critical to the efficient operation of an HVAC system. Valves play a crucial role in regulating the pressure range in HVAC systems and protecting the actuators from letting the pressure reach its maximum level. There are different types of valves used in HVAC, including butterfly valve, gate valve, check valve, air-vent valve, motorised on/off valve and pressure independent balancing control valve.

There are several common problems that can occur with pipes and valves in HVAC systems. Here are some of them:

• Leaking: Leaks in pipes can cause significant damage to an HVAC system.
• Corrosion: Mineralisation, tarnish and wearing will corrode the parts inside your valves over
• Clogging: Clogging is a common problem with valves in HVAC It can be caused by dirt, debris or mineral buildup.
• Freezing: Pipes and valves can freeze in cold weather conditions, which can cause significant damage to an HVAC
• Pressure problems: Pressure problems can occur when the pressure range in an HVAC system is not regulated

Consequently, maintenance of valves and pipes in an HVAC system is crucial to ensure the efficient operation of the system. Here are some general tips on how to maintain your valves and pipes:

• Clean all valves: Cleaning valves is one of the simplest methods to extend their One can use a soft brush or cloth to remove any dirt or debris that may have accumulated on the valve.
• Clean dirt and debris from pipes: In addition, vent pipes should be protected to prevent the entrance of rainwater, which would inhibit valve
• Check for leaks: Leaks in pipes can cause significant damage to an HVAC One should check for leaks regularly and repair them as soon as possible.
• Replace damaged parts: When noticing any damaged parts, such as a damaged pipe or cracked valve body, one should replace them
• Assess valves regularly: Valves should be examined and checked on a regular This will help with identifying any potential issues before they become major problems.
• Perform routine shutdown maintenance: Mineralisation, tarnish and wearing will corrode the parts inside your valves over To prevent this, you should perform routine shutdown maintenance on your valves.
• Lubricate valves: Valves need lubrication to reduce friction and wear on the valve components, thereby extending their lifespan.

CONTROL VALVES IN AN HVAC SYSTEM

Danfoss ABQM DN250 at a local data centre. Image supplied by Automated Control Solutions

Valves are part of the most essential components in an HVAC system, whether cooling water pumps, fan coil units, air handling units or water chillers, in order to control the flow of air, gas and water.

The most common control valves in an HVAC system are the following:

• Butterfly valves, ball valves and plug valves assist in controlling the ventilation and heating of an air conditioner. Others are diaphragm valves, gate valves and knife gate valves.
• Triple-duty valves for cooling and heating hydronics, are a part of many HVAC They simultaneously act as balancing valves, check valves and shut-off valves. There are also automatic flow, limiting valves that control the speed pumping system to regulate water flow in an HVAC unit.
• Some contain pressure reducing valves that control the water pressure in this loop, and/or circuit setter valves that maintain a specific amount of water flow through the piping loop in an HVAC.

Control valves are critical for HVAC systems. They play an essential role in ensuring that they operate efficiently and last for an extended period. HVAC systems contain varying fluids which depend on the pressure range operated by actuators. Control valves assist in controlling the forces regulating the pressure range in HVAC systems. They prevent the actuators from letting the pressure reach its maximum level – once pressure starts touching the upper limit, the valves divert excess oil to bring the pressure down. In addition to this, valves also help release cracking pressure in HVAC fluids.

The control valve plays a crucial role when it comes to pressure overriding in an HVAC unit. On the one hand, it regulates cracking pressure that allows HVAC fluids to pass quickly. But on the other hand, it also allows full-flow pressure into the HVAC unit. Together, they help improve the efficiency of your HVAC system significantly.

SAFETY RELIEF VALVE REPLACEMENT, MAINTENANCE AND INSTALLATION

Safety relief valves are relatively maintenance-free devices, though periodic visual inspection should be made to verify the condition of the valves. While performing this inspection, some of the conditions to watch for are:

Signs of corrosion that could make a valve malfunction

• Broken or missing seal wires
• Valve leakage
• Missing nameplate
• ‘Stacked’ relief valves

The New Danfoss ABQM4 FCU Valve. Image supplied by Automated Control Solutions

A major question concerning relief valves is, when and how often should the system relief valves be changed? They should be changed out after discharge to ensure safeguarding a system with a properly set relief valve. Most systems are subject to accumulations of piping debris such as metal shavings and solder impurities, as the system is fitted for installation. These impurities are generally blown into the relief valve seats at the time the valve is discharged. The impinged debris then inhibits the relief valve from reseating at its original set pressure. Valves are then found to relieve at considerably lower pressure settings than the stamped valve setting, due to the force of the reclosing action.

The International Institute of Ammonia Refrigeration (IIAR), in its Bulletin 109, IIAR Minimum Safety Criteria for a Safe Ammonia Refrigeration System, recommends that the relief valve be replaced or inspected, cleaned and tested every five years.

ANSI STD K61.1-1989, Safety Requirements for the Storage and Handling of Anhydrous Ammonia, is very specific in its requirements. Paragraph 6.8.15 states:

“No container pressure relief devices shall be used after the replacement date as specified by the manufacturer of the device. If no date is specified, a pressure relief valve shall be replaced no later than five years following the date of its manufacture.

REFERENCES

1. IIAR
2. https://www.achrnews.com/articles/94640-safety-relief-valve-replacement-maintenance-and-installation
3. https://www.sciecom/ articles/61696/20200730/what-is-the-function-of-control-valves-in-an-hvac-system.htm
4. https://www.com/resources/articles/best-practices- pipe-and-valve-selection-for-cooling-system