Calibrating your heater

This post is the third one of a series about controlling by a home automation controller the house heating system described in the first post.
The control systems installed in heaters are fundamentally different from those 20 years ago. Electronics is managing entire device, and it permits to implement sophisticated regulation algorithms.

But due to sophisticated regulation, heater settings are more complex. Improper adjustment of them may have disastrous impact on performance and thermal comfort, increasing then energy consumption.

When building our house, this is a person dedicated to the tuning of the boiler who took control on settings. After 1 hour of installation the full installation was working. Without real testing, those parameters settings shouldn’t match in all cases, these are “standard” settings . After a while I’ve rechecked those parameters.

How to optimize power consumption ?

The rule is simple: the water circulating in the pipes must be the least hot as possible. This applies for heating network as for the domestic hot water system.

Why a lower water temperature reduces consumption ?

• because the energy lost by the heating system is proportional to the difference between the room temperature and the water temperature in pipes
• in the case of a gas boiler, the condensation mechanism is even better than water to be heated is less hot
  

• in the case of a heat pump, performance’s also following the same trend. Compare, for example the COP for hot water at 35 ° C and 65 ° C :
  

Another phenomenon is however to be considered. For a too low water temperature, the boiler circulator will operate continuously to keep the temperature of the house, which will lead to an overconsumption of electricity. This is also the thermal comfort of the home that may suffer.

The modern condensing boiler

The condensing boiler now includes a complex control system using a plurality of temperature sensors. If we have a look at Chaffoteaux Tania Green boiler, it includes internally 2 sensors per circuit (inbound temperature, outbound temperature), then 4 sensors for 2 circuits.

The inbound and outbound temperatures are sufficient to regulate thermally a home if the conditions are constant. The temperature difference between those is proportional to the energy delivered in the house. If the temperature difference is low, then the boiler should stop heating. This is a particularly effective way to regulate for high inertia heating systems such as underfloor heating.

Of course conditions are varying, especially the outdoor temperature changes from season to season. The amount of energy to provide inside the house is proportional to the temperature outside. The outdoor temperature sensor adapts the outbound water temperature in regards to outdoor temperature. Now perfect heating temperature regulation is possible if the water rule is optimal.

However there are also other source of energy inside the house that are varying quickly : electrical appliances (oven, hob), solar gain, human presence. The indoor thermostat takes into consideration those variations with a quick reaction time.

To Summarize this, the 3 different kind of regulation types that have to be put in place are :

1. stop heating if the temperature of the inbound water is close to the outbound temperature
2. establish a water rule using an outdoor temperature sensor, and optimize settings
3. use an indoor thermostat to finely regulate the indoor temperature

We’re going to focus on step 2, optimization of water rule.

Optimize water rule

The water rule can only be checked if indoor thermostat is disableb. The easiest way to do this is to set a high setpoint (eg 26 ° C). If the temperature regulation is set correctly, the internal temperature is stabilizing and varying slightly. It’s then correctly regulated in relation to the outdoor temperature.

To perform the test:

1. do the test in a season where heating is required and outdoor temperature’s varying  widely between day and night (beginning of winter).
2. Set the thermostat to a very high temperature to block its action
3. Record the indoor and outdoor temperatures throughout the day. (Thanks to my smarthome system and my eedomus controller)
4. Analyze data, make configuration adjustment of the boiler settings
5. Restart the test another day if the results are not yet optimal

Most of time my indoor temperature setpoint is between 20 ° and 21 °. So I’ve tuned parameters in order to have indoor temperature to stabilize at 22 ° C with indoor thermostat disabled.

Two parameters have to be tuned :

• the variation of hot water temperature according to the outdoor temperature.
  We have then to tune the slope of control of the outbound water temperature versus  outdoor temperature.
  In the case of Chaffoteaux Talia Green, it’s parameter number 422 for heating zone 1.
  The slope giving the most stable temperature throughout the day has to be selected
• the average indoor temperature during the day.
  We have to globally increase or decrease the reference temperature of the outbound hot water.
  In the case of Chaffoteaux Talia Green, it’s parameter number 423 for heating zone 1.
  The setting that provides the desired indoor temperature have to be selected (22 ° C)

Conclusion

It took me 3 days to optimize my heating system parameters, with a quick analysis of data and parameter adjustment each night. I finally changed a single parameter : the slope (parameter 422), which I increased from 1.5 to 2.0.

This change may not have any influence on consumption, but it improved comfort. The default setting set by the fitter was indeed too optimistic and didn’t allow to keep a constant temperature in case of low temperatures. Thanks to correction, we have never ever had this feeling of cold house.

The fitter can’t evaluate the thermal performance of a house when making the initial settings. It therefore applies the standard settings that can’t be optimum for all houses. A home automation system records the temperature history, it provides the tools to change methodically settings for a specific house.