Demand side response (DSR) in district heating

21.04.22 12:58 PM Comment(s) By mkyrola

Demand side response of district heating network

There are great savings hidden in the demand side response in district heating

Written by Sonja Salo. Published earlier by Fourdeg Oy at Mon 10 Sep 2018 11:00:00 AM EEST

This article was previously published in Kuntatekniikka (12/2016).

Equipping the heating system of buildings with intelligent control devices can bring significant economic and environmental benefits. Once the buildings are connected to the local district heating network of cities or municipalities, the buildings should not be optimized individually, but the entire district heating network as a system that simultaneously optimizes production, distribution and consumption.

About half of Finnish homes are connected to district heating. Total energy consumption in 2015 was about 33 TWh, down 5 percent from the previous year, due to record warm weather.

District heating has been considered the most cost-effective way to heat buildings, especially in urban areas. Finland, like other Nordic countries, has some of the world's most comprehensive district heating networks. However, alternative forms of heating are evolving at a rapid pace. Increasing competition and changes in the direction of energy policy are putting great pressure on district heating companies to change.

District heating is currently produced directly to meet consumer demand and at fairly rigid pricing. District heating consumption varies both seasonally and daily according to outdoor temperature and consumer behavior. Flexibility in energy supply is mainly achieved through changes in production, the utilization of large water tanks and the optimization of the distribution network. Momentary peaks in demand often have to be replaced by fossil fuels because they are suited to rapid changes in heat production.

The heat gets stored in structures

Alternatively, the energy consumption of individual buildings could flex downwards during momentary consumption peaks. The purpose of district heating demand side management is to transfer the right amount of thermal power needed by buildings over time, while optimizing the total energy demand of the network. For example, thermal energy can be supplied to buildings a few hours before a peak in demand. The energy supplied is stored either in hot water tanks or in the structures of the buildings, thus reducing the energy demand of the buildings during the peak demand. This avoids the start-up of an expensive back-up power plant.

The demand side management for district heating has similarities to the one used for electricity. Internationally, Demand Side Management is also understood as total energy savings, and Demand Response in electrical systems refers to the transfer of power over time. Unlike electricity, district heating is forced to be produced locally.

District heating is also more rigid as a form of energy, and it reacts more slowly to changes and flexibility must be planned in advance. With intelligent temperature control, the end user does not notice the momentary change in heating due to the slow response.

The ultimate goal of demand side response (DSR) is to achieve savings in both energy consumption and costs without sacrificing ease of use. Therefore, domestic hot water and district heating demand side management has only limited possibilities.

Virtual thermal battery

Buildings connected to district heating can be part of a virtual, distributed heat accumulator with intelligent control. These local small thermal storages appear to the district heating company as one large, virtual thermal battery that can be charged and discharged by the operator in the same way as a large water tank heat battery.

A distributed thermal storage system works like a virtual power plant in electrical systems. In this way, a district heating company can increase its virtual battery capacity with a relatively small investment without owning any physical storage.

The distributed thermal storages can be managed remotely with devices connected to the Internet of Things. Its advantages include low investment costs, predictive maintenance and efficient use of space. A distributed thermal storage in a district-heated property is a substantial heat accumulator.

The heat accumulator charges and discharges into the structures according to the change in room air temperature, enabling a short-term heat storage of about a few hours.

When radiators increase power, the room air heats up first due to lower thermal capacity. Thereafter, thermal energy is slowly transferred into structures of the room, such as the walls, floor, and ceiling.

Correspondingly, as the power of the radiators decreases, the room structures slowly transfer thermal energy into the room air while maintaining a constant temperature.

Thermal storage capacity can be increased

The storage potential of structures depends to a large extent on the thermal capacity of the material, its mass and the thermal gradient to which the storage is applied. The buildings connected to the demand side management should be heavy structured and thus own high thermal capacity.

Thermal storage capacity can be increased by adding latent heat storage (LHS) instead of sensible heat storage (SHS), which can be implemented either by active systems or by passively integrating the phase-change materials into the structures.

Equipping a building with intelligent controls reduces a building’s energy consumption as controllers balance the interior temperature of the rooms, lower the temperature during absence, and learn the individual thermal capacity of the building. With the right control, the building optimizes and saves energy.

With demand side management, the internal temperature of a building may rise momentarily, causing heat losses to rise. The building may therefore consume more energy than it saves during the heat outage. However, this increased energy demand has been realized during a cost-effective period and the total cost of energy production may still be decreased.

Power can be cut by up to 30%

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Energiateollisuus (2015) Energiavuosi
Sonja Salo (2016) Predictive Demand-side Management in District Heating and Cooling Connected Buildings,
Kärkkäinen et al. (2004) Demand side Management of the District Heating Systems
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