HeatingSystem

Problem Description

The heating system is relatively new, but has two problems:

1. During spring and autumn, it does not heat enough, leaving the house too cold.
2. When the other rooms have a nice temperature, the living room is still a little bit too cold.

We solve Problem 1 by adjusting (increasing) the desired room temperature in autumn and spring through the Buderus control device. However, this often has to be adapted as outside temperature changes, and it often gets too warm or too cold in the house as a result during these times.

We solve Problem 2 with blankets.

Problem Analysis

Problem 1:

The Buderus system computes the necessary water temperature based on outside temperature and desired room temperature.

The heater starts heating the water that is constantly pumped through the house heating system when it is below this desired temperature. While heating the water, it tries to reach the desired water temperature by regulating the stream of natural gas that is burned. Apparently the maximum gas flow is 100%, the minimum gas flow while still heating is somewhere around 33%. During spring and autumn, it quickly happens after every heater start, that the temperature of the water leaving the heater exceeds the desired water temperature even at the lowest possible gas flow of around 33%. In response, the Buderus system stops the gas flow entirely, only to start the heating again some 30 seconds later. This leads to an enourmous number of gas ignitions during the day (several 100), which quickly resulted in a broken burner in the Buderus heater after 2 months of the first autumn where we needed the heating system.

As a mitigation to reduce the number of flame starts per day, the minimum interval between flame starts has been increased to 14 minutes, which limits the number of flame starts to 100 per day. The effect is that the second burner still works, but the house is too cold during autumn and spring if we leave the desired room temperature unchanged. Apparently the Buderus controller does not try to reach the desired water temperature on average, but regards the desired water temperature as a maximum, and always shuts down the burner when this is exceeded for a few seconds. Our current mitigation is to increase the desired room temperature, which causes the Buderus controller to compute an increased needed water temperature, which results in an increase of the average water temperatur that is closer to the one we need.

Problem 2:

In the heating water distributor, the water flow throttle for the living room is already set to max throughput. Still, the resulting temperatur in the living room is noticeably cooler than in the other rooms. We will have to investigate different options to mitigate this problem. Options are:

• Again increase desired room temperature in the Buderus control. Then,
  • either adjust the themostats in all other rooms to have them close the valves when the other rooms are already at their disired temperature.
  • Or adjust the flow throttles of all other rooms to reduce the water flows through these.

For the first option, we need better thermostats in all the rooms. The current analogue thermostats have a coarse 1 to 6 scala with no apparent relation to temperatur in °C. I believe the ideal solution would be to first implement the thermostat based solution, then analyze which thermostats close how often, and based on that, reduce their throttle settings in the water distributor.