# Predicting internal temperature with or without HVAC

1. Dec 29, 2016

### Claude_mar

Hi,
how to predict indoor temperature with or without HVAC? I have the internal temperature's value, the external temperature's value and the temperature of HVAC's air output. I want two function, one with HVAC on and other with mode off.
Hp: start time 0,
end time Tend.
Tend has values from 0 to 12 hours.
The calculation is approximated. I do not need a detailed formula, but approximated. I apologize for my bad English.

2. Dec 29, 2016

### Staff: Mentor

Welcome to PF!

The temperature without HVAC is roughly equal to the average outside air temperature.

The temperature with HVAC is dependent on the total insulation value (in units such as watts per degree C) of the building and the heating or cooling capacity (in units of power, such as watts) of the hvac system.

Those are steady-state values. For time varying, you need to know the heat capacity of the building in watts per degree C...which is really difficult.

What is the purpose of your questions?

3. Jan 1, 2017

### Claude_mar

Thank you,
I want to realize a HVAC's control; I need an approximate formula to predict indoor temperature. For example, internal temperature is 24 degrees, the HVAC is OFF and the external temperature is 18 degrees. Which is temperature after 30 minutes? This is the first form of prediction. The correct prediction is made with another form. The approximation can be great. How can I do?