TechniSolve Software

coils are the most common air cooling equipment

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Once you have calculated the heat load and done the psychrometrics and ducting, you 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.

We have written a number of coil designers to make the calculations easy.

Chilled Water Coil

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.  You can edit this field but you would probably find it easier to use the fin & tube editor.  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.

The barometric pressure has an effect on the coil performance since it controls  the amount of moisture.  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.  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.

Right click in the fields area a pop-up menu will appear.  This allows you to do the following:

1. Plot the process on the psy chart.
2. Set typical air conditioning conditions.
3. View the manufacturing report.
4. View the solution diagnostics.

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.

Hot Water Coil

Apart from the fluid temperature range, the HOT WATER COIL is essentially the same as the chilled water coil described above.  The design temperature difference, is always indicated as a positive value.

Direct Expansion Coil

To solve the performance of refrigeration systems, you will need to calculate the performance of the direct expansion and air cooled condenser coils.

All of the coil types are designed to exchange heat between some fluid and air.  The direct expansion coil is a refrigerant coil that is used to cool air.  The fluid in this case is an evaporating refrigerant.  

By supplying a low temperature liquid refrigerant to the evaporator, heat is absorbed from the air to boil the liquid.  The heat is the called the latent heat of vaporization and can be visualized by looking at the Mollier Chart for the particular refrigerant.

In solving a direct expansion coil, the problem is to determine the film coefficient for the refrigerant.  This is complicated since the mode of boiling is not easily to determine.  We have assumed film boiling where there is a uniform vaporization of the refrigerant.

The program allows you to select from one of the many refrigerant types and calculate the duty.  Notice that in this program, you can set the refrigerant temperature.  In practice, this temperature is a result of the balance between the compressor, the condenser and the evaporator.  This is a complicated process but our RefSim program does all this for you.

Air Cooled Condenser Coil

This program is the companion to the direct expansion coil.  In the vapour compression cycle, the air cooled condenser recieves super-heated vapour from the compressor.  The purpose of the condenser coil is to reject heat from this hot refrigerant gas to the ambient air.  Sometimes, you would even use this heat by rejecting the heat into the room air.

As with the evaporator coil, you can set the refrigerant temperature in the condenser coil program.  The actual balance point will depend on the matching of components at operating conditions.  As the ambient temperature changes, the condensing temperature will therefore change.  When making a design, you would select a condensing temperature to ensure that you don't exceed the limits of the compressor or the refrigerant type.

As with all of the other coil types, the air side is common.  You may wonder why we include the wet bulb temperature with the on coil.  The reason is that we use a common moist air state form to enter the air temperature.  This editor allows you to specify the state of the moist air by any two properties.

The other coils in the set are the steam heating coil and the hot water coil.  These are both heating coils and are based on the same style as the programs shown above.

Steam Coil

The steam coil is basically an air cooled condenser coil using water as the tube side fluid.  In this case, the steam condenses from saturated vapour to saturated liquid.

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