In general, metering of district heating consumption in ultra-low temperature district heating (ULT DH) systems is not different from traditional district heating. However, when electricity is used to boost DHW temperature, this share of the DHW production is no longer metered by the district heating company,or must be metered separately by an additional electricity meter.
There might be different ways to bill the consumer. One option is that the consumer is just billed the district heating consumption with usual tariffs, and then pays the additional electricity consumption over the general electricity bill. Though, this typically results in higher costs for the consumer as electricity is typical priced higher than district heating. Another option is that the district heating company is compensating the consumer for the costs of the electricity consumption used for boosting. A third option is that the tariffs of ultra-low district heating can be adjusted to reflect the system advantages of using ultra-low temperature and thus compensate the electricity consumption for boosting. In this section, we will first take a look at general metering and billing practices and then finally discuss specific ultra-low temperature challenges and options.
Meter per dwelling or per building
In multi-dwelling buildings with collective heating systems, the district heating meter can be placed at the interconnection with the district heating systems and the collective substation that provides space heating and DHW. Alternatively, meters can be placed in the individual dwelling in combination with an individual substation (flat station). In the first case(A), electricity for boosting may be included in the general metering of the building’s shared electricity consumption or can be measured separately typically at relatively low costs. In the individual dwellings(B), the electricity for boosting may be included in the general metering of electricity or can be measured separately by an additional electricity meter.
Modern district heating meters have various properties:
Smart meters are mostly referred to as meters giving the option to register energy consumption on an hourly basis which allows for billing based on hourly prices. Further, there must be a communication of these data to the trader of energy which relief the reading and reporting of the meter stand. In other words, the smart meter must be remotely read.
Other intelligent meter applications include e.g. leak surveillance detection or sensor fault detection
Billing information and frequency
The information on the energy bill should explain and reflect the tariffs which apply to the district heating system. Some tariffs are a fixed contribution per year, others are variable tariffs where the final bill will depend on the actual use of energy or other measurable entities. The fixed tariffs may reflect the fixed costs of the district heating scheme, including the appreciation on the assets, and the variable part the variable costs. But it is not necessarily so. Billing based on just variable tariffs exists as well. The questionnaire sent to the project partners has confirmed that.
The frequency of billing is typically based on the amount of consumption. Customers with smaller consumptions will typically be billed interim 3-4 times per year with a yearly calculation of the actual consumption, and the large consumers more often e.g. on a monthly base. The introduction of smart meters, also for customers with smaller consumptions, makes it applicable to provide bills more often. The district heating company may provide the consumer with a web-interface or an app to look up its own consumption. Monthly bills may be sent by the means of electronic communication. In principle, future billing can be done down to the hour in case the meter resolution and communication/remote reading allows.
Variable district heating tariffs may be related to the energy and the transport costs of supplying the district heating to the consumer.
Variable district heating tariffs
Variable district heating tariffs may be related to the energy and the transport costs of supplying the district heating to the consumer. Transport costs are in some sense equivalent to the costs the electric distribution system operator (DSO) charges for distributing electricity:
In case the district heating tariff is based on volume only, this is to some extent a combined energy and transport tariff. In the case of the transport tariffs, these can take advantage of some of the additional calculated meter parameters available in modern heat meters such as the ‘Supply energy’ and ‘Return energy’.
Fixed district heating tariffs
Compared with the transport tariff mentioned in the previous section, district heating tariffs can also include a fixed part attributed to the capacity provided. This can be a fixed tariff based on the living area of the building or it can be a tariff based on the heating power capacity provided. Another capacity tariff exists as well. Besides, a fixed tariff is sometimes also put on the heat meter related to the lifetime cost of metering. This fixed meter tariff is sometimes denoted as a subscription of the meter. Other administrative costs can be included in the fixed tariffs as well.
When boosting the temperature with electricity, the electricity consumption as metered is multiplied by the electricity tariff to get the number to be billed.
When boosting the temperature with electricity, the electricity consumption as metered is multiplied by the electricity tariff to get the number to be billed. The electricity tariff can, as for district heating, typically consists of variable parts taking into account the traded electricity and the transport on the distribution (DSO) and transmission (TSO) level. Fixed parts may include a subscription to the meter as well as other administrative costs. Besides, different taxes may be part of the electricity tariff. The roll-out of electricity smart meters in Europe will facilitate the use of hourly tariffs which are expected to be variable in a wider range in the future due to the massive introduction of renewable fluctuating electricity production plants such as wind turbines and PVs.
When connecting a building to the district heating system, the new customer would typically have to pay for the connection/branch pipe based on the actual enterprise costs. Different incentive schemes may apply when introducing a new district heating network to an area. The connection fee may also include a lump sum e.g. taking into account the administrative costs associated with getting a new customer.
When applying ULT DH to an area, the district heating tariffs should optimally reflect the benefits of ULT for the district heating system. This may imply that the district heating company is operating with two different tariff structures –one for traditional district heating and one for ultra-low temperature. A non-exhaustive list of general benefits is:
Thus, optimally these benefits should be divided into variable and fixed ULT DH tariffs as well as the connection fees. A threshold between when to apply the traditional and the ULT-tariffs can be based on the ULT-definition used in the RELaTED project:
District heating systems that supply district heating to the customers at a temperature level where the production of domestic hot water requires a supplementary heat source to deliver satisfactory domestic hot water temperatures. The supply temperature limit will depend on national requirements set to prevent legionella bacteria growth in domestic hot water systems. Though all district heating systems supplying district heating at temperatures below 50 °C will be considered ultra-low temperature district heating systems (ULT DH).
Supplying district heating for low energy buildings and applying ULT also introduces challenges that can be handled in the tariff structure and billing practice: