Delta T in Chiller: Ultimate Guide

If your chiller systems are experiencing inconsistent cooling performance or rising energy costs, then one of the main problems is poor Delta T management. For optimal performance, you must maintain Delta T within the recommended threshold.

In this article, we will explore some of the most critical variables about this change in temperature – from calculation, classification and optimization processes, among critical variables that can help improve chiller efficiency.

What is Delta T in Chiller?

Delta T, featured in a chiller, refers to the temperature variance of the water as it enters the chiller versus when it leaves. This value is typically obtained by subtracting the supplied water temperatures from the returned temperature.

This value is not standardized across all devices with chillers; instead, it varies depending on the system requirement. However, 5.5°C is the most common Delta T featured in typical chillers.

How to Calculate Delta T

The ideal Delta T in chillers varies depending on the exact design of the chiller. Chiller Delta T calculation involves the following steps:

• The first step is to measure the temperature of the return water
• Next, measure the temperature of the water supplied to the chiller
• Lastly, deduct the temperature of the water supplied from the temperature of the water returned.

The formula is therefore: ΔT =return water temperature−supply water temperature.

For example, if the water supplied is 7.3 °C and the water that flows from the chiller is 13.3°C, then using the formula, the delta temperature would be 13.3−7.3=6°C.

Why Change in Coolant Temperature Matters

From chemical processing and food processing facilities to plastic manufacturing, maintaining Delta T is non-negotiable. It will directly affect the energy consumption and cost of operating chiller systems.

From our experience, Delta T will increase compressor runtime, which increases wear and tear which ultimately resulting in higher cost of chiller maintenance. Additionally, this will reduce the chiller cooling capacity and cause process temperature fluctuations.

By monitoring Delta T chiller operators and companies can identify cooling inefficiency early enough before resulting in costly downtime.

Types of Delta T in Chiller Systems

· Design Delta T

This is the chiller system’s Delta temperature, as is calculated under optimal conditions during engineering, as well as sizing, as intended by the manufacturer. As an operator, this value acts as the guideline on what is recommended by the manufacturer, although it is expected to vary based on system utilization. Unlike the operational Delta temperatures, this category is typically a standard set, and optimal functionality is determined by how close the variance is to the expected value

· Normal Operating Delta T

This temperature variance is established under normal operations, which often involve varying conditions, but it is the most accurate reflection of a chiller’s Delta T. Given that operating conditions vary from one machine to the next, depending on environmental conditions, among other things, this variance is expected to fluctuate. While variances are expected, the chilled water temperature difference should remain close to the expected design Delta T.

· High Delta T

A high Delta T will cause systems to absorb more heat from various industrial processes before chilled water returns to the chiller. This scenario is recommended for high-load applications where the main intention is to maximize cooling capacity while reducing pumping energy.

However, when Delta T is extremely high, it can be problematic for the chilling system. It can be a problem in other chiller system problems such as fouled heat exchangers or restricted water flow.

· Low Delta T

For most industrial chilled water systems, low Delta T is always the biggest challenge. Ideally, this implies that the system is transferring less heat to the chilled water, which consequently forces the chiller pump and compressors to “overwork”.

Therefore, if you are operating a plastic injection molding or pharmaceutical facility, a persistent Delta T can reduce process reliability, thereby increasing operating costs.

Causes of Low Delta T

There are various causes of reduced Delta T, and it most often indicates a system-wide problem rather than a localized problem. It primarily signifies that the chiller is not picking up enough heat to efficiently cool it down.

Main causes include;

• If the valves regulating the flow of the water are impeded or completely fail, it can result in excess water flowing into the chiller. The excess water, in turn, reduces the temperature of the return water as well as the Delta T.
• When the heat transfer surfaces get contaminated by dirt or the formation of scales, then the layer of contamination forms a barrier that reduces the transfer of heat, thereby reducing the Delta T.
• If your machine is oversized, the low delta T can be experienced as the system compensates for its size by pumping excess water.
• Water flow should be properly balanced to ensure that the cooling water can access all the parts required for even cooling. If it doesn’t cool down properly, then some sections may experience reduced Delta T.
• In some cases, low Delta T is expected given the light load being processed; in that case, even if it is below the design Delta T, it does not indicate a problem.

How to Measure Delta T in a Chiller

To get an accurate Delta T value from your chiller, you can either use a thermometer or built-in sensors, depending on the type of machine that you have. For a functional reading, take the temperatures during operations under your typical environmental conditions.

Measure the temperature of the water at the inlet, and that will be the return water temperature. The temperature is measured at the water outlet, and this will be the supply water temperature. Then subtract the temperature of the supply from the return, and the resulting value is the Delta T.

How to Troubleshoot Delta T Problems

During the troubleshooting process, the maintenance team should evaluate the entire cooling system rather than focusing on the chiller system. Identifying issues like fouled heat exchangers, excessive water flow or improperly controlled valves can help reduce inconsistent cooling,

• The first step in identifying the problem is to accurately measure the return and supply temperatures, ensuring that it is done correctly to get the correct readings.
• Subtract the supply from the return temperature to get the Delta T and compare it against the design Delta T to identify if it is higher or lower.
• Next step is to check the rate of water flow, pump operation and bypass paths to ensure that the water flow is optimal. Excess water flow can result in low Delta T.
• You can then check the control valves. Poor valve control, failed multi-way valves, or stuck valves can cause reduced Delta T.
• Inspect the surfaces of the coils and heat exchangers to ensure that they are not contaminated
• Check the system balance to ensure that its performance is optimized across all systems and the load requirement is met.

FAQs

How does ΔT affect chiller energy consumption?

The lower the Delta T, the higher the energy consumption as the system compensates.

Can ΔT be too high?

Yes, the temperature can be elevated beyond the design Delta T as a way of compensating for system loads or as a result of a system problem.

Why does Delta T affect chiller efficiency?

Reduced Delta T minimizes efficiency, as less heat is transferred, requiring more energy to maintain system requirements.

How often should you check the chiller coolant temperature?

You should conduct inspections routinely during operations.

Is Delta T different for air-cooled and water-cooled chillers?

Although they are used for the same function, they operate differently.

What is the difference between Delta T and approach temperature?

Delta T defines the variance between chilled water return temperature and supply temperature. Approach temperature defines the variance between the heat exchanger’s fluid and the refrigerant saturation temperature.

Experiencing Low Delta T or Rising Cooling Costs?

ChillerOne experts will help you to analyze your chiller systems and recommend the right solutions. Whether your facility uses air-cooled chillers or water-cooled chillers, we provide custom solutions to maximize cooling efficiency, reduce energy consumption and improve long-term operational reliability – talk to ChillerOne experts now.