4 Advice to Choose a hydraulic oil chiller manufacturers

Here are the four basic factors that affect chiller sizing and selection:

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1. Desired coolant temperature. This is the coolant temperature at the inlet of your process or equipment. It is important to measure the temperature at this point to allow for coolant heating as it travels from the chiller to the process. The longer the distance to be covered, the higher the potential heat gain. This heat gain can be minimized by insulating the cooling line and positioning the chiller as closely as practical to the equipment or process being cooled.

2. Heat load. This is the amount of heat that needs to be removed. It is usually expressed in BTU/hour or watts. The heat load value is often provided by the equipment manufacturer. If not, it can be calculated using the following formula:

Heat load   = Flow rate x Fluid density x Fluid specific heat x Constant x ∆T°

BTU/hour

Watts

Flow rate

=

Gallons/minute

Liters/minute

Fluid density

=

Pounds/gallon

Grams/liter

Fluid specific heat

=

BTU/pound°F

Joules/gram°C

Constant

=

60

0.

∆T° = the difference between the inlet and outlet temperatures of the equipment being cooled

=

°F

°C

Properties of Common Cooling Fluid

Fluid

Fluid Density

Specific Heat

Lbs/gal

Grams/liter

BTU/lb°F

Joules/gram°C

Water @ 77° (25°C)

8.333

1

4.181

50% water, 50% propylene glycol @ 50°F (10°C)

8.744

.25

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0.835

3.493

50% water, 50% ethylene glycol @ 50°F (10°C)

8.992

.72

0.776

3.245

It is generally recommended that 20 to 50% be added to the calculated heat load to provide a safety factor if the chiller will be operated at ambient temperatures above 68°F (20°C) or at high altitude, or if the heat output of the device is variable. This will also provide a margin of safety for future cooling needs. That said, resist the temptation to build more of a safety margin into your chiller than is necessary; an oversized chiller will not cool your equipment any more effectively but will cost more to purchase and operate.

3. Coolant flow and pressure. These parameters are normally provided by the equipment manufacturer and are a function of the surface area and the heat transfer characteristics of the process/material being cooled. It is crucial that your chiller deliver coolant at the proper flow rate and pressure — if the flow rate or pressure is too high, the equipment being cooled may be damaged; if it is too low, the heat removal will be inadequate. Your chiller supplier can help you specify the type and size of coolant pump most suitable for your needs.

4.   Condenser heat dissipation. The final factor influencing chiller/heat exchanger selection is how the heat removed will be dissipated. Devices with air-cooled condensers exhaust heat into the surrounding air and require only power and ventilation for operation. Devices with water-cooled condensers transfer heat to the facility’s cooling water supply. Chillers with remote condensers (i.e., the condenser is located outside the facility) are also available. These are quieter, require less space, and do not add heat to the building interior, thus reducing summer cooling costs. However, they are more expensive to install and are not easily relocated.

Naturally, there are other factors — such as heating capability, remote temperature tracking, DI water capability, etc. — that affect how a chiller is ultimately configured. Conscientious chiller vendors will take all these into consideration when helping you select the best chiller for your particular application.

Be prepared to provide the following information when contacting your chiller supplier:

• Desired coolant temperature at the inlet to your equipment or process
• Anticipated heat load, as calculated or specified by the equipment manufacturer
• Cooling fluid flow rate and pressure requirements
• Internal heat dissipation, space, and portability needs
• Special requirements, such as remote temperature tracking or DI piping

Among the most compelling reasons for a chiller installation is minimising downtime through the continuous protection it provides in removing heat from valuable and temperature-sensitive process equipment. At the same time, a chiller saves water and associated costs by recirculating and re-using the plant’s own water supply.

The cost of cooling water can add up quickly, especially if process equipment is running for several shifts a day. When a chiller is introduced into the system, it can bypass the costs and need for a monitored, municipal water supply and wastewater discharge, and contribute to substantial savings within production budgets. Furthermore, with the latest developments in chiller technology, capital investment payback can be realised over a very short period of the equipment lifetime.

The main factors to bear in mind when considering the appropriate cooling fluids for a process are their performance characteristics and their equipment compatibility. The performance of a cooling fluid is based upon its properties at a given temperature. The relevant parameters are specific heat, viscosity, and freezing/boiling points. There is a direct relationship between specific heat and cooling capacity. In order to maintain system integrity and prolong optimum performance, mixing a percentage of ethylene or propylene glycol with water (typically in the 10 to 50% range) is recommended when low or high setpoint temperatures are required.In terms of compatibility, the potential for corrosion and the early degradation of seals are common failure modes for incorrectly sized systems. That is why the materials of construction and the nature of fluids should be an important consideration, and why inclusion of a corrosion inhibitor in the cooling fluid is recommended.

However, in the latest developments of chiller technology, the storage tank and hydraulic parts of centrifugal pumps are constructed in stainless steel to prevent process water contamination with rust particles, as well as provide higher levels of reliability and temperature control. Similarly, state-of-art, all-aluminium microchannel condensers are designed to provide long life without corrosion and require 30% less refrigerant charge in comparison to other types of heat exchanger.

The setpoint temperature will affect the cooling capacity of a chiller. Decreasing the temperature will put more load on the refrigeration system, and vice versa for increasing it. There is a direct relationship between the temperature at which the chiller has been set and its total cooling capacity. Therefore, it is important to review the chiller’s published performance data for relevance to the proposed installation.

At the same time, if the chiller is destined for an exposed site, it is equally important to establish the level of freeze protection required, i.e., the coldest leaving fluid temperature of the chiller during operation.

While pump life is a primary consideration when configuring an industrial cooling system, pressure loss across the system and the necessary flow rate must first be determined by the pump size and performance. 

Pressure: An undersized pump will reduce the fluid flow rate through the entire cooling loop. If the chiller has been equipped with internal pressure relief, the flow will be diverted around the process and back into the chiller. If there is no internal pressure relief, the pump will attempt to provide the necessary pressure and run at what is referred to as dead-head pressure, or limit. When this state occurs, the pump’s life can be drastically reduced; liquid ceases to flow and the liquid in the pump becomes hot, eventually vaporising and disrupting the pump’s ability to cool leading to excessive wear to bearings, seals, and impellers. 

Determining the pressure loss across a system requires siting pressure gauges at the process’s inlet and outlet, then applying pump pressure to obtain values at the desired flow rate. 

Flow rate: Inadequate flow through the process will yield inadequate heat transfer so the flow will not remove the heat necessary for safe operation of the process. As the fluid temperature increases beyond the setpoint, the surface/component temperatures also will continue to rise until a steady-state temperature that is greater than the initial setpoint is reached. 

Most chiller systems will detail the pressure and flow requirements. When specifying the necessary heat load removal as part of the design, it is important to account for all hoses, fittings, connections, and elevation changes integral to the system. These ancillary features can significantly increase pressure requirements if not sized appropriately.

Ambient Temperature. An air-cooled chiller’s ability to dissipate heat is affected by the ambient temperature. This is because the refrigeration system uses the ambient air/refrigerant temperature gradient to induce heat transfer for the condensation process. A rising ambient air temperature decreases the temperature differential (ΔT) and, subsequently, reduces the total heat transfer. If the chiller uses a liquid-cooled condenser, high ambient temperatures can still have negative effects on key components such as the compressor, pump, and electronics. These components generate heat during operation, and elevated temperatures will shorten their lifetime. As a guideline, the typical maximum ambient temperature for non-exterior rated chillers is 40°C.

Spatial Constraints: In order to maintain the proper ambient air temperature, it is important to provide adequate air circulation space around the chiller. Without proper airflow, recirculation of an inadequate volume of air rapidly heats it up. This affects chiller performance and potentially can damage the chiller unit.

Selecting a correctly sized chiller is a crucial decision. An undersized chiller will always be a problem – never able to properly cool the process equipment and the process water temperature will not be stable. In contrast, an oversized chiller will never be able to run at its most efficient level and prove more costly to operate.

To determine the correct size of unit for the application it is necessary to know the rate of flow and the heat energy that the process equipment is adding to the cooling medium, i.e., the change in temperature between the inlet and outlet water, expressed as the ∆T.

The formula for calculation purposes is: Heat energy per second (or more commonly known as Power) = mass flow rate × specific heat capacity × change in temperature (∆T)’ The specific heat capacity of the water is nominally expressed as 4.2 kJ / kg K but if it contains a percentage of glycol additives that value is increased to 4.8 kJ / kg. K Note: 1K = 1°C and the density of water is 1 i.e.,1l of water volume = 1kg of water mass. Here is an example of the formula application to determine the correct kW sized chiller to handle a water flow rate of 2.36 l/s (8.5 m3/hr) with a temperature change of 5°C. Heat Energy per second (kJ/s or kW) = 2.36 l/s (Flow Rate) X 5°C (∆T) X 4.2 kJ /kg K (Specific Heat Capacity of pure water). Chiller size required = 49.6 kW. Alternatively, the heat load to be cooled may already be known in which case the formula can be re-arranged to determine the temperature difference (∆T) that can be attained with different flow rates (achievable with different pump sizes). There may be other circumstances that can influence size choice.

Planning for future plant expansion, exposure to high ambient temperatures, or location at high altitudes, could all lead to the specification of a different size of unit.

In the latest, advanced generation of industrial chillers, ease of maintenance, operational safety, and intelligent control and connectivity are prominent features of their designs.

For example, they are constructed with IP54-rated, sound-attenuated canopies that allow chillers to operate indoors or outdoors, even at ambient temperatures down to -45°C. They are specifically designed for easy access to the installed components − refrigeration systems in the front and the cooling water circulation assembly in the back. Wide canopy doors and intelligent layout reduces maintenance time and allows for easy inspection to prevent breakdowns. Innovative new models on the market feature a wide range of safety devices, such as flow and level switches, thermal probes, pressure probes, crankcase heating and strainers which allow the chiller to operate securely.

Additionally, a fully hermetically sealed refrigeration system prevents refrigerant gas from leaking and requires zero maintenance. UK FGAS Regulations do require an annual, and on larger refrigeration systems, bi-annual inspection by a FGAs certified engineer. The provision of a phase sequence relay ensures no risk of compressor damage in case of incorrect wiring. In these new designs, a touch screen controller operates with energy-efficient algorithms, combines all the chiller sensors into one system and issues timely warnings in case of deviation from the operating parameters.

Full connectivity is achieved with built-in smart remote monitoring capability on chiller sizes 11 Kw and above. This provides user’s machine data, in real time, in a clear format to ensure optimum efficiency.

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