CASE

TUAS building district heating demand control

According to a district heating demand control pilot project done during winter 2014-2015 demand control measures did not have effect on the indoor temperatures experienced by the users. Approximately 30 MWh energy savings were accrued.

TUAS building houses for example the Departments of Industrial Engineering and Management as well as Automation and Systems Technology.

Fortum and Aalto University Properties carried out a district heating demand control pilot project in collaboration with Aalto University in October-May 2014-2015. The goal of the project was to find out how adjusting the district heating, i.e. using demand control, affects the indoor temperatures and user satisfaction. By using demand control the temporary demand peaks can be balanced, and so using fossil fuel based power plants can be reduced. Heating can also be directed to cost-optimal times.

In district heating demand control the supply water temperature can be temporarily lowered by certain degrees. During the pilot project the water temperature was lowered by 5-20 °C degrees 1-4 hours at a time. The typical demand control was 2 hours with 5-15 °C degrees reduction. At the largest the water temperature was decreased by 20 °C degrees 2 x 4 hours per day.

The project utilized a new smart heat control system (Fidelix), which controls the supply water temperatures of the radiator and ventilation network, gets the outdoor temperatures with its own measuring system, and receives the district heating prices for the next day once a day. After that the system directs the temperature of the supply water at a suitable time according to pre-set temperatures.

Indoor temperature

Temperature information was collected from the building automation system with 20-minute interval. Altogether 195 090 room temperature samples were recorded from fifteen office rooms. 143 066 other temperature measurements from outdoor and supply air were recorded.

Operative temperature was measured in six rooms during one month with a ten-minute interval. Altogether 12 629 operative temperature samples were taken into consideration. The measurement was done to find out how the temperature information received from the system matches with the temperature felt by the user. The operative meter was placed as close to the real working place of the user as possible.

According to the temperature measurements the effect of the demand control to the temperature changes of the coldest rooms has been minor, at the largest 1.04 °C degrees. However it is good to notice that the winter was exceptionally warm.

In the fifteen rooms under measurement there was a clear difference in how demand control affects their temperatures. In seven rooms (mainly corner rooms) the temperature change was clearly faster than in the other rooms. In addition there were clear changes in temperature decrease depending on the timing of the demand control. Because of these changes the possible temperature changes in certain rooms caused by the demand control are greater depending on the outdoor temperature.

The standard deviation of the operative measurements was in all six cases greater than the equivalent TAC system measurement. This means that the temperature felt by the user is in reality greater than the measurements of the TAC system assume.

There were clear changes in room temperatures during weekdays also when demand control was not used. The reason for these changes is probably ventilation, other heat sources such as people and computers and great outdoor temperature changes.

User satisfaction

The temperature satisfaction of users was followed by a monthly online survey and a ’happy-or-not’ machine placed in the building lobby. 3 957 happy-or-not survey responses and 139 online survey responses were collected.

In the survey there was not a direct connection between demand control and user satisfaction. User satisfaction was greatest with deepest demand control measures (-15 °C and -20 °C) and with -5 °C measures satisfaction was at its lowest. With -10 °C measures user satisfaction did not differ from normal. It seems like user satisfaction depends more on functionality of the building automation system, right settings and other things affecting temperature changes. User satisfaction also depends on the personal characteristics and location of the work place.

“Savings need to be assessed over longer term and building specifically. For both Aalto University Properties and Fortum it is crucial that there are enough buildings taking part in the demand control. Then remarkable savings can be accrued in heating costs and demand control becomes part of heating production optimization”, says area sales manager Susanna Huuskonen from Fortum.

“Users of TUAS building participated actively in the pilot and gave valuable feedback on indoor temperature. Based on the results the demand control measures could be done without them affecting the user experience on temperature. Active participation of the users in pilot project steering group is necessary for smooth project implementation”, says Satu Kankaala, Development Manager, Environment and Sustainability at Aalto University Properties.

The results of the pilot showed that by using demand control savings in both energy consumption and costs can be accrued without compromising comfort. The pilot also showed how important collaboration is in advancing energy efficiency.