Part 3 of this series of articles outlining the development of an Android app for the HVAC market focuses on additional functionality added to v3.0 of the app. See part 1 and part 2 of the article for an introduction to the evolution of this app.
The two key additions include additional refrigerants as well as the ability of the app to compute sub-cooling.
Like superheat, Sub-cooling is an important parameter and is indicative of the state of the sealed system. In order for an air-conditioning system to work correctly all of the refrigerant in the condenser must condense into a liquid. Sub-cooling is a measure to indicate the temperature difference between the saturation temperature of the refrigerant and the actual temperature of the liquid refrigerant before it enters the expansion device.
Please see part 1 if the article for a brief explanation of how the vapor compression cycle works.
The figure below shows how sub-cooling is measured
In general sub-cooling is used to charge a system with refrigerant when the expansion device is a Thermostatic Expansion Valve (TEV) whereas superheat is used to charge systems in a fixed orifice expansion device such as a piston or capillary tube.
Since v 1.0 of the app focused on target superheat the second page only contained calculations for the actual superheat for the system as computed by the app. With the addition of the sub-cooling calculation the app can now cater to service personnel working on both fixed orifice as well as expansion valve based devices.
Below is a screenshot of the second page in v3.0 of the app.
The second column of values show the fields needed to perform a sub-cooling calculation. The high side pressure would the pressure read on the manifold gages at the condenser and the Liquid Line temperature would be the temperature of the refrigerant line taken as close as possible to the expansion device.
The calculate button computes both the superheat and subcooling at the same time. As a precaution against undefined values appearing the results fields the app provides default vales on startup which can then be modified by the user.
In addition two new checkboxes marked “Dewpoint” and “Bubblepoint” have been added. Many of the new refrigerants added to the app are known as blended refrigerants.
Without going into the deep details of refrigerant chemistry many older refrigerants are being phased out due to the fact that when released into the atmosphere they damage the ozone layer. Many newer refrigerants which do not harm the ozone layer tend to be blended refrigerants which are made up of two or three single compound refrigerants. These refrigerants due to their compound makeup evaporate and condense over a range of temperatures. This spread is known as temperature glide.
When working with such refrigerants the point at which it begins to condense and evaporate are different and are described tow two distinct sets of data. Depending on the equipment manufacturer it is reasonable to use one of the boundary values or an average of both when performing superheat and sub-cooling calculations.
The Dewpoint and Bubblepoint checkboxes allows the use to select the use of the boundary value or the average value. By default the average value is used but the user may override this by checking one or both of the checkboxes.
To modify the app the relevant xml layout files were modified to incorporate the new layout needed to encompass the superheat and sub-cooling calculations.
The app may be found on the Google play store at https://play.google.com/store/apps/details?id=com.apps.bmc.superheatcalc
For any further information or questions please email Ravin at email@example.com