Compute the thermal characteristics of your house

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Antori91
Posts: 102
Joined: Sunday 12 February 2017 18:12
Target OS: NAS (Synology & others)
Domoticz version: 4.97&3.5
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Compute the thermal characteristics of your house

Post by Antori91 » Thursday 21 June 2018 15:01

Hello,

By using two temperature sensors (indoor and outdoor) and an energy usage sensor, you can calculate with Domoticz the thermal mass (C), the thermal loss (H) and the cooling / heating rate (k) of your House. Such project is embedded in my home automation project http://www.domoticz.com/forum/viewtopic ... 38&t=17032.

Once you have calculated such constants, you can answer questions like:
- 1 / If I stop heating now, how many hours / days before the indoor temperature reaches the outside temperature?
- 2 / If I start heating now, how many hours / days before the indoor temperature reaches the setpoint?
- 3 / How much energy I will use to heat my house the next hour?
- 4 / Is it true I always make money when I stop heating, even for a short period of time?
- ...

Thermal modeling of buildings is not really easy to understand (at least for me). There is a whitepaper here: http://www.mdpi.com/1996-1073/10/9/1358 . You do not need to read the entire whitepaper, but focus on chapters 3 and 4 which provide the theoretical context.

Using Domoticz, the H calculation is really simple, I use a virtual sensor and divide the total energy used during a day by the number of Degrees.Day of the day. This must be done when heating is on with a constant indoor temperature (i.e. steady phase with an indoor temperature equal to the setpoint).

I found k a little bit more complicated to calculate. I use also virtual sensor and moving average (4 hours with temperature readings every 5 minutes) to smooth out the ratio (indoor temp - indoor temp 5 mn ago) / (indoor temp 5 mn ago - outside temp 5 mn ago) variations. This should be measured when the heating is off and the indoor temperature decreasing (i.e. the outdoor temperature is below the indoor temperature).

Then, C (thermal mass) is also easy to calculate (H / k).

Now, you can answer to the questions (Tout is outdoor temp, Tsp is setpoint, To is your initial indoor temp and P the Power of your Heating Appliance) :
Question 1 : 1/k days,
Question 2 : ∆t in days = ( C * (Tsp - To ) ) / ( P - H * ( (To+Tsp)/2 - Tout ) )
Question 3 : assuming your indoor temp is at the setpoint (steady phase), E(W.h) is H * (Tsp - Tout)

This is more for now an on-going project. My end goal is to build a heating optimizer for my house not only based on schedule (like it is today) but enough smart to use such constants and be more aggressive in the optimization process.

Any comment/help is welcome
k.JPG
k.JPG (93.78 KiB) Viewed 563 times
Attachments
k.JPG
k.JPG (93.78 KiB) Viewed 567 times
k.JPG
k.JPG (93.78 KiB) Viewed 568 times
Last edited by Antori91 on Saturday 30 June 2018 8:27, edited 11 times in total.
Domoticz High Availability Cluster: Synology Dz V3.5877 (Main) - Raspberry Dz V4.97 (Backup) - Scripts Node.js
Alarm server: Raspberry - motionEye - iot_ALARM-SVR Node.js
Sensors/Actuators: ESP8266-Arduino
https://github.com/Antori91/Home_Automation

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Antori91
Posts: 102
Joined: Sunday 12 February 2017 18:12
Target OS: NAS (Synology & others)
Domoticz version: 4.97&3.5
Location: France
Contact:

Re: Compute the thermal characteristics of your house

Post by Antori91 » Thursday 21 June 2018 15:33

Theory and calculations:
Theorie.JPG
Theorie.JPG (147.83 KiB) Viewed 725 times
H_ThermalLoss.JPG
H_ThermalLoss.JPG (89.65 KiB) Viewed 576 times
Attachments
Indoor_Outdoor_Temp.JPG
Indoor_Outdoor_Temp.JPG (58.7 KiB) Viewed 576 times
Domoticz High Availability Cluster: Synology Dz V3.5877 (Main) - Raspberry Dz V4.97 (Backup) - Scripts Node.js
Alarm server: Raspberry - motionEye - iot_ALARM-SVR Node.js
Sensors/Actuators: ESP8266-Arduino
https://github.com/Antori91/Home_Automation

kimhav
Posts: 75
Joined: Tuesday 01 October 2013 8:31
Target OS: Raspberry Pi
Domoticz version: 4.9895
Location: Malmo, Sweden
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Re: Compute the thermal characteristics of your house

Post by kimhav » Friday 17 August 2018 9:53

Nice project! Going to totally look into this over the next couple of weeks.
Member of Domoticz Sweden Telegram Group

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