Fahrenheit & Celsius- Conversion Rounding off Strategy

3 Minute Read

| Overview

With 75F's system usage globalization implemented, installers, facility managers, and users are allowed to set the preferred units for visualizing the building-level parameter data. Following this, the 75F system had another challenge to address:

Maintaining the integrity of the preexisting system while converting and rounding off values from Fahrenheit to Celsius and vice versa.

| Challenges Faced

The challenges faced were surrounding the desired temperature, current temperature, and tuner rounding.

The desired temperature setting options in the devices and portals were programmed to increment or decrement by 0.5 Fahrenheit and when the equivalent steps were implemented for operation in Celsius, the resultant values did not satisfy the conditions for a 'dual set point temperatures' concept of the system (the 70°F-74°F, heating desired and cooling desired temperature concept).

To solve this, a reasonable rounding technique for the converted values had to be introduced.

| Rounding Strategy for Desired and Current Temperatures

The rounding strategy that was implemented to mitigate this issue is a HALF_UP or HALF_DOWN rounding to be taken for Desired Temp changes.

In this system, the converted values are rounded off to the closest upward whole number when the initial value contains a .6/.7/.8/.9

Similarly, the converted values are rounded off to the closest downward whole number when the initial value contains a .1/.2

Lastly, when the converted value contains a .3/.4 it gets rounded off to a .5

Below is a Common Conversion and rounding examples for current and desired temperature conversions when the values are converted from Fahrenheit to Celsius:

Fahrenheit Value	Celsius Value	Current Temp Round Off Value	Desired Temp Round Off Value [0.5 based]	Precision Percent Lost [Percent error]
75F	23.8889C	23.9C	24C	0.41666666666667% error
67.5F	19.72222C	19.7C	20C	1.5% error
70.3F	21.27778C	21.3C	21.5C	0.93023255813953% error
70.1F	21.16667C	21.2C	21C	0.95238095238095% error
50.4F	10.22222C	10.2C	10C	2% error
30F	-1.11111C	-1.1C	-1.0C	10% error
100F	37.7778C	37.8C	38.0C	0.52631578947369% error
110F	43.3333C	43.3C	43.5C	0.45977011494254% error

Below is a Common Conversion and round-off examples for current and desired temperature conversions when the values are converted from Celsius to Fahrenheit:

Celsius Value	Current Temp Fahrenheit Value	Desired Temp F Round Off Value [ O.5 based]	Precision Percent Lost [Percent error]
23C	73.4F	73.5F	0.1360544217687% error
23.5C	74.3F	74.5F	0.26845637583893% error
20C	68F	68F	0% error
20.5C	68.9F	69F	0.14492753623188% error
26C	78.8F	79F	0.25316455696203% error
26.5C	79.7F	80F	0.375% error
28C	82.4F	82.5F	0.12121212121211% error
20.3C	68.54F	68.5F	0.058394160583951% error

| Rounding Off Strategy for the System and Zone Level Tuners

When it comes to the tuners which deal with the temperature values, the conversion for the tuner values from Fahrenheit to Celsius is handled using the concepts below.

There are two kinds of conversions that are implemented for the user preference of temperature for the tuners:

Absolute Value
Relative Value

The below table elucidates the concepts of absolute value and relative values:

Absolute Value:

For tuners like the CoolingAirflowTemp, HeatingAirflowTemp, etc. which refer to one particular value which is absolute and there is no comparison involved, the conversion is done in the standard way as in the example on the right:

Example:

CoolingAirflowTemp (⁰F) = 60 ⁰F. Now to convert the same to Celsius it uses formula C = 5/9 x (F-32). Therefore, the CoolingAirflowTemp is 16 ⁰C (approximated to the nearest whole number as per the 'Fahrenheit to Celsius Conversion of Current and Desired Temperature' table shown above)

Relative Values:

For tuners like the coolingDeadband, unoccupiedZoneSetback, etc. which refer to a range and not a particular value and are thus considered relative, the conversion is done in as in the example on the right:

Example:

unoccupiedZoneSetback (⁰F) = 2 ⁰F. Now to convert the same to Celsius it uses the formula C = F/1.8. Therefore, the unoccupiedZoneSetback is 1 ⁰C (approximated to the nearest whole number as per 'Fahrenheit to Celsius Conversion of Current and desired temperature' table shown above)

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| Overview

| Challenges Faced

| Rounding Strategy for Desired and Current Temperatures

| Rounding Off Strategy for the System and Zone Level Tuners

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