How to handle Coil Calculation Results Differences?
Coils is a standard software which has been built and developed in more than thirty years basing it on our knowledge and especially on our customers’ feedbacks: the most of the AHRI or EUROVENT certifications have been successfully obtained by many coil manufacturers companies at the first attempt, without any needs to recalibrate the software.
Anyway, sometimes our customers report to us that the coil performances are not in agreement with their experience. We continuously verify and improved Coils calculation engine, so what is the reason of this difference?
There could be two cases:
- Coils outputs are different from the ones obtained with other calculation software
- Coils outputs are different from the data obtained with a specific laboratory test
In the first case we can suggest firstly to check if the inserted geometries and coils shape are exactly the same, and check which is the “standard” layout for the coil that the software considers: on Coils for example the airflow and the fluid flow configuration represent a cross-flow but the calculation is based on a counter-flow: if the number of rows are lower than two this assumption is not real, so the calculation will be affected and the results could be not so reliable (in this case you will be advised by a warning message).
Furthermore, other software (especially coils builders’ software) often use commercial factors in order to increase the total capacity obtained. This means for example that if the user has to design a refrigeration unit, during the coil design stage the user will choose/design a smaller coil in order to obtain the project coil requested capacity, so he will save material and money and he could offer to his customers a cheaper unit: with a favorable economic conditions the customers will accept the offer with more probability. This “trick” could often work because the design is always done in “security” so the coil has always a bigger capacity than the real requested one. Obviously this is not the real situation: only with experimental data you can be sure if the software calculates the real performances of the coil, in fact the certifications institutes (AHRI, EUROVENT, etc..) absolutely don’t allow the use of regulating factors inside a software which have to calculate the performances of certified coils.
Anyway in the standard Coils version there is the possibility to set some factors in order to adjust the outputs: obviously we are sure that the software can calculate the most reliable results for usual coils without any need to modify these factors, but you could have some special no-standard configurations/calculations which may need to set some different values to reach the real output values: in these cases you could modify the factors with your experience or better if you have some experimental data.
One example could be a bended U-shaped coil, typically used in the remote condensers in many air conditioning plants in order to get more compact units. Here the fan is placed over the finned pack and intakes the air from the outside, so the resulting airflow distribution is not homogeneous along the coil, for example across the curved areas the crossing airflow is less, resulting in a low performance of the exchanging surface of those areas. Unilab Coils doesn’t manage this particular geometry configuration, but this problem can be easily fixed: in fact, in the software you can set a special “Security Factor” as 0.85 as a “first attempt” in order to consider the real situation, but you can change it later if the results are still far from your expected capacity.
