I have included a collection of notes that we have pulled together over the years that guide us through typical coil selections for custom air handling units. Thank you. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Sign Up Today. With air at your back which side hand are the headers on? Less pressure drop. Spiral Fin has advantage in steam heat coil as separate tubes can handle higher thermal expansion.
Belled ends allow for larger U-bends and less pressure drop. With glycol the WPD goes up significantly with higher FL so probably need to break big coils up into shorter length sections.
This is called moisture carry-over. We design to avoid this. Face dampers may be needed to control air flow. Leave a Reply Cancel reply Your email address will not be published. Categories Ask DAC.
Chilled Beams. Featured Posts. Current News. MK Plastics. Themo Composite.The fin-and-tube heat exchanger is probably the most common piece of equipment found in any air-conditioning installation. These heat exchangers are typically referred to as coils and are designated by the fluids in the tube. So, a chilled water coil is a fin-and-tube heat exchanger used for cooling air where the coolant is chilled water and the direct expansion coil is a fin-and-tube evaporator found in a vapour compression cycle.
These two coil types are primarily used to cool air. The consequence of this is that there will be condensation on the coil surface and this condensate is clearly evident by the water flowing out of the drain pans of many installations. Methods to design and select heating coils are based on an overall heat transfer coefficient multiplied by the appropriate temperature difference.
In cooling coils where there is condensation, the temperature difference is not the correct driving force since the latent heat of condensation is not accounted for. There have been different ways of dealing with this shortfall. These include the introduction of a sensible heat factor to modify the outside film coefficient, use of a log mean enthalpy difference and the effectiveness method based on a saturation specific heat.
In this paper, we develop the equations and by simulation, illustrate the validity of the effectiveness method for solving wet surface cooling coils. The idea is that the heat exchanger has a pre-defined heat transfer coefficient and that the driving force for heat flow is the temperature difference. The difference in a heat exchanger is that the temperature of the fluids changes significantly.
Without going into the details here, it can be shown that the effective temperature difference for parallel and counter flow configurations can be calculated from the following equation.
In the case of a cross flow and multi-pass configurations, you would have to apply an additional correction factor. The problem with the LMTD method is that the fluid leaving conditions must be known in order to calculate the duty. Clearly, if you know the leaving conditions, then you already know the duty. This makes the performance calculation of an existing coil an iterative process. It turns out that the effectiveness can be derived for many of the common heat exchanger configurations.
These are well known and published in most heat transfer books in the form shown in Figure 1. Figure 1. Effectiveness of a single pass counter-flow heat-exchanger.
If we break the heat exchanger into a number of small pieces, it would be possible to calculate the heat flow at each step without making any assumptions. Figure 2. Thermal model of dry cooling. At the end of the cycle, the water inlet temperature must be compared with the known inlet water temperature and the initial guess revised until a solution has been found.
Dealing with condensation When the surface temperature falls below the dew point temperature of the air, there will be condensation.
This complicates matters since the energy balance must now include the mass and energy flow of the condensate. This means that there are two energy equations on the air-side, accounting for sensible and latent heat. By incorporating the enthalpy potential, we can now simulate the performance of a cooling coil with condensate.
In Figure 3, we see that the surface is wet and therefore the enthalpy at the surface is that of saturation air at the surface temperature. Figure 3. Thermal model of wet cooling coil.How to calculate the cooling capacity of a chiller.
Chillers provide chilled water which is then used to provide air conditioning within buildings. There is a video tutorial at the bottom of the page also.
A recommended website to look these properties up is: PeaceSoftware. Let look at how to calculate the cooling capacity. Metric units: The water flow rate of chilled water into the evaporator is 0. We add The Specific heat capacity Cp is measured in units of kJ per kg per Kelvin. The average temperature is A good website for this is peacesoftware.
Hi Paul, Good day. Need your advice on heat recovery system from water chiller to heat water in building for hot water supply. Requirement parameters are: 1 heat circulating water from ambient inlet 27 degC to supply outlet 60 degC; 2 current chiller design 35 kW; 3 chilled water supply inlet Hot water supply to roof storage tanks usage 12 cu. Also, the heat loss on a 50mm diameter with 25mm insulation over a distance from chiller to roof storage tanks is est.
Like to ask. For instance a chiller is connected to 4 AHU. Reason for having this assumption is if my chill water temperature and flow is optimise, my chiller will work lesser to produce the output which is chill water. Hello sir, i have a chiller tr if chiller running 12 hours per daysit is possible may we count line loss kwh to kwah, and reply for minimum line loss. I am trying to figure out my chillers cooling capacity at variant outlet temperatures, while maintaining the same ambient temperature.
As well as how to calculate the aluminum finned type heat exchanger. Please suggest use. The water originates from a well in the ground and returns to after running through the air handlers.
Does the water run around the coils? Do you have a diagram. Is there a wat to clean the coils that the well water runs through. The water originates from a well in the ground and returns to the well after running through the air handlers.
Is there a way to clean the coils that the well water runs through. Hii paul, thanks for explaining in detail, can you please tell us the working of economizer in a chiller unit. Or am I missing something? Usually it depends on the motor that we include in the system, If its a hp motor then the power consumption would be x 0.Log In. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
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Chiller Cooling Capacity – How to calculate
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Students Click Here. Related Projects. As the coil no increases from 4 to 6 or 8, the gap becomes less and can cause a high bypass factor. What implications should be taken care while the no of rows is decided. Thanks in advance. Sensible heat capacity becomes less as the number of coil rows increase. How does that connect to the sensible heat capacity that too inversely.
More coil rows increase air contact time and remove more moisture. More coils also means more air pressure drop and more work for the fan s. You don't want to blow condensed water back into the air stream. So would it be correct to understand that In a coil where more rows are available will be for the Latent heat removal or dehumidification. Will the both section be available in the same frame of the coil or the coils for sensible and dehumidification are different set of coils with their respective rows and spacing accordingly.
Yes more rows will mean more moisture removal, it also means more sensible cooling and a lower discharge air temperature. And as I mentioned earlier more pressure drop for the fan s to overcome resulting in a less efficient system. The number of rows you have is not the only variable in selecting a coil. You need to also consider number of fins per inch, fin material and whether or not protective coatings are needed. All these will impact a coil's capacity to one degree or another increasing or decreasing the capacity.
For example you may be able to reduce the number of rows by increasing the number of fins per inch or using a different fin material. The best advice I can give you is to take your load calculations, air flow rate, and any special requirements i. There is to my knowledge no magical equation to determine the best coil design, number of rows, fins per inch, etc. Each coil manufacturer can vary these to provide the amount of cooling you need.Once you have calculated the heat load and done the psychrometrics and ductingyou will need to select cooling plant.
The most fundamental of these is the coil. In airconditioning applications, the coil is a fin and tube heat exchanger designed to transfer heat to or from the supply air. If you build up refrigeration systems, you will need to combine an evaporator and condenser coil with a compressor.
This can be done with our RefSim program. The chilled water coil designer gives very flexible control over inputs. The first field is the coil size. This is complicated since there are many values that define a specific coil.
Click on the property button at the end of the field and an easy to use editor will let you set each of the variables independently. This in turn affects the latent heat when changing air states and consequently the total duty.
If you enter the air volume, the face velocity will be updated. It should then be no surprise that the air volume will be updated if the change the face velocity.
The coolant in this case is water. If you press the properties button on the coolant field, you will be able to modify the properties to include any of the usual anti-freeze fluids. In addition, you are free to manually specify the properties to suit any desired fluid. The fluid control option allows you to specify the water temperature difference or the water flow rate.How to calculate the evaporator TD for refrigeration and air conditioning
Clearly you can't fix both. The tube velocity and the water flow work in the same way as the airflow and face velocity described above.
Finally, you can calculate the duty. But there are other options. The calculate field allows you to specify the duty and let the program automatically calculate the size. If you prefer the use different units, simply right-click on the units field and select from any of the posible unit sets for that field.
Cooling Coil Calculations
Right click in the fields area a pop-up menu will appear. This allows you to do the following:. It is well worth looking at the diagnostics, particularly after making a non-standard selection.
This will give some confidence in the result since it will show the full calculation breakdown.First time here? Check out the Help page! I have a problem with water coil sizing. I set the following parameters for cooling and heating:.
Therefore, through the formula cooling :. You are correct up to a point. The water coil model does result in a design capacity very near your calculations. However, that capacity is only used to calculate a coil UA value. Other coil parameters are also calculated during this sizing effort, such as bypass factor, SHR, etc. The model then changes the inlet conditions to nominal values to determine what physical coil would be used for these application input parameters i.
Realize now that your coil inlet air temperature was 32 C. This physical water coil would have a much higher capacity if the inlet air temperature was increased from The result is the actual physical coil you would specify for your application i.
Thanks a lot! Just to be sure I understood right: does it mean that the sizing is correct but in the report is given with different reference values? I'm modelling an AHU from its technical specifications so I wanted to be sure about it. You coil is sized correctly according to your inputs.
I would check the results using report variables for node temperatures before and after the coil to assure things are working correctly.
I had the same problem in another model but this time this is causing a lot of problems and unmet hours. Is there a way to force the cooling coil sizing? In this new case I have a fan coil cooling water coil. My input correspond to W but I find W in the report and also in the simulations so that the mean air temperature is always over the setpoint.
Please start posting anonymously - your entry will be published after you log in or create a new account. Asked: Cooling minimum air flow fraction? Failed to match against any enum values. Chiller oversizing problem in eQuest.Your tank dimensions in inches:. Electrical input into your tank:. Operating conditions of your tank:. Operating temperature of the tank.
Sizing Heating and Cooling Coils
Help F. Temperature of coolant. Solution In Tank This calculator will help you find the size of coil you will need as well as the material best suited for your coil see material selection chart and disclaimer.
This unique calculator can be used for cooling as well as heating applications. After finding the coil that fits your tank, request a quote from MBA with a touch of a button! Operating temp. Coil source temp. Selecting tank solution - Your coil material is determined by the type of solution to which your coil will be exposed. It is extremely important to choose your tank solution properly.
If your tank solution is not on the list, please select "Other" from the list. If you are using a proprietary solution in your tank, please consult your chemical supplier for proper choice of coil material.
Material Disclaimer - Material suggested on this web site provide general guidelines only. In view of the ever increasing amounts of proprietary chemical solutions being offered by chemical suppliers, we suggest that you contact your chemical supplier and follow their recommendation in selecting the most suitable material for your specific application.
Tank agitation - Agitating the solution in your tank improves heat transfer properties and might lead to smaller coils. Agitation also enhances the corrosion resistance of metal.
Custom Air Handling Units | Coil Selection Guidelines
Toll Free: 1. What is your application? Cool tank using cold water Cool tank using Freon Your tank dimensions in inches: Length Width Depth Electrical input into your tank: Volts Amperes Operating conditions of your tank: Operating temperature of the tank. Help F Temperature of coolant. No Yes. Cool tank using cold water Cool tank using Freon. Select the solution in your tank select "Other" if it is not in this list :.
Is the solution in your tank agitated?