In Europe, approximately 40% of the total energy consumption is used in buildings. Providing a comfortable and healthy indoor environment for occupants is responsible for a major part of the energy used in buildings. Demand response can be utilised in different ways within heating and ventilation of buildings to reduce or time shift the energy consumption on both utility and consumer level. During demand response control, some of the indoor environmental parameters are affected. These parameters include, e.g., room air temperature or air quality (which relates to ventilation practices and emissions from people and materials.
Hence, demand response is a bargaining process between energy consumption and an acceptable impact on the indoor environmental quality. Since Europeans spend around 90% of their time indoors, the indoor environment affects occupants’ comfort and health significantly. DR programs shall preferably not compromise residents’ experienced indoor environment too much, as this will jeopardise their acceptance of these programs.
In Denmark, 64% of all households are connected to the district heating grid. Like the electricity grid, the district heating grid is challenged by periods with a high consumer demand, so-called peak loads. In dwellings, for example, there is a peak in the morning, when there is a simultaneous demand for space heating and hot water for the morning activities, especially showering. For various reasons, the district heating suppliers would like to make it possible to time-shift some of the heating in dwellings away from this morning peak. The most important reason for this is that the suppliers in various areas are experiencing a growing heat demand due to new-built homes that are being connected to the grid.
This means that the suppliers either have to invest in upgrading the district heat system, which might cost a lot of money and make the heat more expensive for customers, or alternatively find ways to time-shift some of the consumption away from the peak hours.
One way to time-shift some of the consumption away from the peak hour in the morning is to install equipment in homes that can control the heating. In this way, the residents and/or the supplier of district heating can turn off the heat shortly during the few hours with peak consumption, e.g. between 6 and 9 am. Of course, only with the prior acceptance from the residents. Such a set-up will be tested at the Danish pilot site of the RESPOND project. Here 20 apartments with central heating in a social housing settlement will be used for demonstration. The apartments is situated in a settlement of terraced houses of flats, erected in 1975.
The heating system is using hot water directly from the district heating grid, i.e. there is no heat exchange and no buffer tank with hot water. Therefore, the thermal mass of the building is used as a buffer to allow to time shift the consumption.
Thermal simulations of the dwellings in the Danish pilot site have indicated that it will only result in a limited drop in temperature during the hours when the heating is switched off due to the heat accumulated in the construction. Roughly, the temperature will drop approximately 1°C per hour, depending on factors like occupancy, solar radiation and where the dwelling is situated in the blocks of flats. To maintain the temperature within a comfortable range for a longer period, the temperature may be slightly raised before switching off the heat. This altogether shows that switching off the heat for a short time (e.g. 3 hours) in the housing block seems feasible as a measure to reduce peaks in district heating in the morning.
Whether switching off the heat, as suggested above, is actually acceptable for residents in social housing needs to be verified in real life scenarios. This will be done through a focus group interview and by testing the concept in 20 dwellings.
In the Danish part of the RESPOND project, a focus group interview with residents has been performed targeting the demand response actions in relation to space heating practices in their homes as described above. The “DR concept” was fairly well received. There was some concern that it would be too cold in the morning. But if it could be controlled so that it is comfortable warm before switching the heat off, and so it is not cold when getting up in the morning, it seemed acceptable. The hardware and the RESPOND app must be simple and flexible to use and allow the residents to decide the temperature level themselves and when, for how long and how much the temperature is allowed to fall when the heat is switched off.
The residents agreed that the concept must be automated, so that they do not have to turn the heat on and off themselves on a daily basis, or as expressed by one of the female residents “I just don’t want to bother and deal more with it, so it just has to run…”.
The residents pointed out that not all weekdays/weekends are identical. Therefore, the idea of being able to “deactivate” the DR settings, for example in the next 24 hours, after which it returns to the DR settings and runs automatically again, was well received. Some kind of information about the indoor environment provided by the app would be appreciated since it is by some considered complex. Another relevant feature in the app that would be appreciated, is some kind of feedback with advices to improve the indoor environment, e.g. airing out if the humidity in the dwelling is high. Including information about the indoor environment (and recommendations for improvements) in DR solutions can be part of making these solutions meaningful and engaging to people.
Figure caption: This figure was used during the focus group interview to illustrate the DR concept of switching off the heat for a limited time in the morning to time shift the energy consumption for space heating without getting outside the comfortable temperature range.
Henrik N. Knudsen
SBi, Aalborg University Copenhagen