Guide To Troubleshooting INEFFICIENT COOLING FANS

Transcription

1 Guide To Troubleshooting INEFFICIENT COOLING FANS

2 TABLE OF CONTENTS Introduction Enclosure Cooling Basics Key Attributes of Enclosure Cooling Symptoms of Poor Enclosure Cooling Typical Cooling Fan Problems How to Troubleshoot Fan Problems and Improve Performance Benefits of Fans When Fans Should Not Be Used Alternative Cooling Solutions Understanding Cooling Fans Next Step

3 INTRODUCTION Today, most electrical enclosures are fitted with enclosure cooling systems in order to remove heat generated by interior electrical equipment. Low-cost cooling fans are a popular choice for ventilating enclosures. However, it s not unusual to find that cooling fan installations are not particularly effective, and, especially in hot weather, maintenance personnel often struggle with the disruptive effects of electrical enclosure overheating. Some telltale signs of inefficient enclosure cooling fans are: Nuisance tripping Unexpected equipment failure Burnt electrical contacts and connections Hot spots PLCs that crash for no obvious reason HMI screens that go dark Excessive dirt inside enclosures These issues can usually be resolved if the prerequisites for effective enclosure cooling are understood. In many instances, all that s required is corrective maintenance. In other situations where there is an imbalance between the enclosure heat load and fan cooling capacity, an upgraded cooling solution is required. In this Guide to Troubleshooting Inefficient Cooling Fans, we will show you: How efficient cooling reduces maintenance time and improves operations Key reasons that a cooling fan may not be performing optimally How to improve fan performance When a fan isn t the right cooling choice Alternatives to fans that can increase overall efficiency

4 ENCLOSURE COOLING BASICS The purpose of enclosure cooling is to remove heat generated by electrical equipment inside the enclosure and to maintain a reasonable internal temperature for safe and reliable operations. As enclosures become too hot, equipment performance diminishes, and equipment can ultimately break down. It s essential to understand that the temperature of an electrical enclosure will increase until there is a balance between the rate of heat generation and the rate of heat removal. KEY ATTRIBUTES OF ENCLOSURE COOLING Heat Load Every electrical enclosure generates heat as a consequence of the electrical losses of the equipment inside the enclosure. This heat load can be calculated by identifying the power consumption of the various electrical devices in the panel. The heat loss must be calculated by multiplying the power consumption of each device by its inefficiency (1 - efficiency) and adding the losses together. Other factors that contribute toward the total heat load include the heating effects of solar radiation i and other external heat sources. Enclosure Temperature The enclosure temperature must be kept below the maximum operating temperature of the equipment in the enclosure. It s better to choose a temperature that is somewhat lower than manufacturers recommend, because this provides a factor of safety and allows for natural temperature variation across the enclosure. Most panel and enclosure cooling manufacturers suggest that the enclosure temperature should be kept below 95 degrees Fahrenheit. 3

5 SYMPTOMS OF POOR ENCLOSURE COOLING The symptoms of poor enclosure cooling are not that obvious and, unless understood, are easily missed. Here are some common symptoms of poor enclosure cooling: Ambient Temperature The maximum ambient temperature that the enclosure will be subjected to must be established, as this represents the worst-case scenario. For outdoor applications, this can often be obtained from national and regional climate records. Care must be taken to differentiate between average maximum temperatures and actual highs; it is the highs that should be used. Calculation of Required Cooling Capacity Once the heat load, ambient temperature, and required internal temperature are known, it s possible to calculate the required cooling capacity. Various cooling options exist. A cooling fan would normally be the first choice, provided the ambient temperature is lower than the desired enclosure temperature. The approximate fan capacity can be calculated by multiplying the heat load in watts by 3.16 and dividing the result by the difference in temperature, measured in Fahrenheit, between the ambient air and the enclosure. The result of this calculation gives the required airflow in cubic feet per minute (CFM), and with this information, the correct fans can be selected from manufacturers catalogs ii. It s important to note that this is an approximate calculation that does not take into account external factors such as solar radiation, heat conduction, and the size of the enclosure, all of which have an impact on the required cooling capacity. A more accurate result can be obtained by using an online enclosure temperature management calculator. iii 4

6 Unusual Equipment Failure Equipment failure may be caused by high enclosure temperature, especially if there appears to be no other obvious cause. Common failure patterns that may indicate excessive enclosure temperature include relay failures, burnt-out contactor coils, and indicator lamp failures. Other signs of overheating are unexplained variable frequency drive problems, DC power supply issues, and failure of electrical equipment. Blown Fuses If there s no sign of a circuit fault, the reason for blown fuses might be that they are too hot. Similarly, the reason for nuisance tripping of switches and thermal circuit breakers may be high enclosure temperatures. Common failure patterns that may indicate excessive enclosure temperature include relay failures, burnt-out contactor coils, and indicator lamp failures. Unexplained PLC Problems If PLCs crash and then work normally after resetting, the reason might be the fact that the PLC processor, memory cards, and other sensor circuits are too hot. Other sure indications of high enclosure temperatures are LCD screens going dark and touch screens malfunctioning. High Enclosure Temperature If the enclosure appears to be too hot, it probably is; the actual air temperature should be checked using a thermometer. When investigating electrical-enclosure equipment failures, always consider the possibility that the failure was caused by a high enclosure temperature. 5

7 Typical Cooling Fan Problems Cooling fan problems can be summarized in three categories: 1. Fans are not working properly. 2. Fans are inefficient. 3. Fans are insufficient. If a fan is not running or not working properly, it may be faulty, but it s always best to check that nothing has tripped and that there are no loose connections. There are many reasons why a fan may be inefficient or not performing properly. These include obvious problems such as the fan running in the wrong direction, blocked or inadequate filters, and air leaks. Also, the airflow may be restricted for some other reason. So before assuming a fan is insufficient, check that nothing is affecting its proper operation. It is possible that the fan is insufficient and not capable of properly cooling the enclosure. A common reason for this is that the ambient temperature may be higher than was anticipated during the enclosure design. A fan can only remove heat from an enclosure, and it cannot bring the internal temperature below ambient temperature. Consequently, the enclosure temperature will always be a few degrees higher than that of the outside air. This means that the temperature of a fan-cooled enclosure is closely related to the ambient temperature. In many areas, peak outdoor summer temperatures frequently exceed 90 degrees Fahrenheit, while in the Central and Western regions of the USA, it s often above 100 degrees Fahrenheit. Under such conditions, a fan may just not be enough. The fan may be too small to dissipate the heat generated in the enclosure. This could be because heat load calculations were either not done or they did not adequately take all factors into account. Possibly, additional equipment might have been subsequently installed, increasing the total heat load. 6

8 How to Troubleshoot Fan Problems & Improve Performance It s best to adopt a systematic, logical approach to troubleshooting cooling fan problems to avoid coming to the wrong conclusion. First, ascertain that the fans are working. Second, identify and rectify any reasons why performance is inefficient. Finally, if the previous steps don t resolve the problem, establish why cooling is insufficient and use this information in order to upgrade the enclosure cooling. Always refer to the technical manual when troubleshooting fans. iv Fans Not Working If the fans are not working, establish why: Fuses: Check for a blown fuse or tripped circuit breaker. Power: Ensure that there is power available at the socket. Cable: Confirm that the connections are properly made and that the cable is sound. Supply voltage: Make sure that the supply voltage is correct. Switches: Establish that the control switch is working, and if a thermostat or door isolation switch is used, check that it operates correctly. Faulty fan motor: If the fan has power but doesn t run, it is faulty and should be replaced. Poor Performance If the fans are working, find out why they aren t cooling properly: Fans: Check the fans for sticky bearings and broken blades. Airflow: Make certain that the fans are running in the correct direction. Hot air rises, so the airflow should be from the bottom to the top. Filters: Ensure that the filters are clean and replace them if they are blocked. Sealing: Make certain that the enclosure doors close and seal properly and that there are no holes in the enclosure allowing air to bypass. Make certain that the filters are properly seated, especially if there s a lot of dust inside the enclosure. Obstructions: Confirm that there are no internal obstructions, baffles, wiring harnesses, shelves, or debris that are causing an internal airflow restriction. There should be at least five inches of clearance around the fan inlet and outlet to ensure an unrestricted air supply. Equipment layout: Use a thermal camera in order to identify areas of poor airflow and hot spots. Take note that variable frequency drives and power conversion equipment generate a lot of heat and must receive a good supply of cool air. Check that the hot air from these drives is not directed toward sensitive equipment. 7

9 Fans are Insufficient If the existing fans are working correctly, but the enclosure is still too hot, it s possible that the fans are too small or not suitable for this application. Reasons include: Heat load too high: The panel may be generating more heat than the fans can handle. Perform a heat load calculation to establish the required cooling capacity and select an appropriately sized fan. High ambient temperature: If the ambient temperature is higher than the required enclosure temperature, a fan is the wrong solution, and an enclosure air conditioner will be required. Filters clogging: If the environment is excessively dusty or damp, causing clogging of filters, clean the filters more often. If this does not work, a ventilated enclosure may be the wrong choice, and a closed loop cooling solution would be better. There are several reasons why fans should always be the first choice for enclosure cooling. They are easy to install, they take up very little space, and a wide selection of fans is available in order to accommodate high heat loads Benefits of Fans There are several reasons why fans should always be the first choice for enclosure cooling. They are easy to install, they take up very little space, and a wide selection of fans is available in order to accommodate high heat loads. Fans purchase prices are low, and running costs are negligible. They are suitable for NEMA v Type 1 and NEMA Type 3 ventilated enclosures and can be used indoors and outdoors, provided filters are fitted with weather-protecting shrouds. vi Even when used indoors, fans should always be fitted with filters in order to prevent dirt being drawn into the enclosure. 8

10 When Fans Should Not Be Used Despite their simplicity, fans are not the best choice for enclosure cooling in some applications. Fans should not be used in: Hot Ambient Conditions Because fans cannot cool air, they are a poor choice for hot ambient conditions the enclosure internal temperature will always be several degrees above ambient temperature. Although some equipment is rated for use in high ambient temperatures, this is not the norm, and, ideally, enclosure temperatures should not be higher than 105 degrees Fahrenheit. Extreme Weather Conditions In extreme weather, driving wind can cause rain, ice, and snow to saturate filters, limiting airflow and potentially allowing moisture to enter the enclosure. In such conditions, a sealed NEMA 4 enclosure with a closed loop cooling solution would be a better choice. Very Dirty & Dusty Locations High dust loads can overwhelm filters and lead to blockage and poor airflow. In these cases, a sealed enclosure should be used. Corrosive Environments Even the best filters cannot prevent the ingress of corrosive vapors, which frequently cause serious damage to electrical equipment. For these types of locations, the most appropriate solution is a NEMA 4X enclosure and a closed loop cooling solution designed to resist chemical attack. This also applies to marine environments where salt spray is a major problem. Locations Subject to Water Spray Water sprays are often used in food processing plants to wash down equipment. A closed loop cooling solution designed with NEMA 4X protection would be the appropriate choice. 9

11 Alternative Cooling Solutions Cooling fans have two specific limitations. First, they only remove heat and cannot cool below ambient temperature. This means that they are not suitable for use when the ambient temperature is higher than the desired enclosure temperature. Second, fan-cooled enclosures draw outside air into the enclosure along with any dirt, dust, and corrosive vapors that may be present. Although filters will limit what is drawn into the enclosure, they are not 100 percent effective against vapors and will clog quickly in dusty locations. Fan cooling is not recommended in very dirty, dusty, or polluted areas. Two alternative closed loop cooling solutions are available: Air to Air Heat Exchanger This closed loop cooling solution uses a heat pipe in order to transfer hot air from the enclosure to the outside where it is dissipated. An Enclosure Air to Air Heat Exchanger requires no power except for its air circulation fans and is, in contaminated environments, an ideal alternative to fans. vii Enclosure Air Conditioner Air Conditioner Applications are ideal for use in hot locations, and they re equipped with temperature controllers that maintain a stable temperature inside the enclosure irrespective of ambient temperature fluctuations. Additionally, their closed loop cooling design means that outside air doesn t enter the enclosure. viii 10

12 Understanding Cooling Fans The enclosure cooling fan is an efficient and effective choice for cooling electrical enclosures, provided users understand the limitations of fan cooling. It s important to keep in mind that fans remove heat; they do not and cannot cool below ambient temperature. Their efficancy relies on the capacity to remove heat by convection, so filters must be kept clean, enclosure doors kept closed, and obstructions that restrict or divert the moving air avoided. The selection of cooling fans should always be based on the results of heat load calculations; rule-of-thumb estimates need to be avoided. Filters must be installed in order to protect equipment inside enclosures. Bear in mind that cooling fans are not suitable for very hot locations, nor are they a good choice in dirty, dusty, or polluted areas. In these circumstances, a better choice is a closed loop cooling solution, such as an air conditioner or air to air heat exchanger. However, filtered cooling fans are an excellent and economical choice for cooling electrical enclosures where the air is clean and ambient temperatures are lower than the required enclosure temperature. 11

13 Next Steps If you are diagnosing inefficient cooling fans in an electrical enclosure or aren t sure what the best cooling solution is, use the Thermal Edge Enclosure Temperature Management Calculator in order to help find a product with the proper cooling capacity. Then, request a quote and talk to one of our experts about your specific project and application. References i. NREL: Maximum Daily Solar Radiation per Month ii. Climate Prediction Center: Extreme Maximum Temperature USA iii. Thermal Edge: Filtered Fan Packages iv. Thermal Edge: Enclosure Temperature Management Calculator v. Thermal Edge: Fan Technical manual vi. NEMA: NEMA Enclosure Types vii. Thermal Edge: 3R Shrouds viii. Thermal Edge: Air Conditioner Applications ix. Thermal Edge: Enclosure Air to Air Heat Exchanger 12