## 2 Thematic Review and Analysis
### Implementation Strategies
#### 2.6.1 Tariff Structures  
The tariff and pricing system plays a critical role in optimizing heat usage within DH systems. Historically, efforts have focused on promoting the use of heat meters over the strategy as with the annual fees based on the amount of heated space, which do not account for actual consumption [PERSON] et al. (2016). The examination of tariff plans and historical expenses in DH systems is detailed in references [PERSON] et al. (2016); [PERSON] et al. (2016); [PERSON] et al. (2016). This section aims to analyze and develop formulas for tariff structures designed to support lower return temperatures, which are essential for enhancing the overall energy efficiency of DH systems. It is essential to emphasize the experimental measurements reported by [PERSON] and [PERSON] [PERSON] and [PERSON] (2016), which compare the temperature drop recorded by customer installations under two different tariff structures at various supply temperature levels (see Figure 15). The authors observe that the volumetric flow rate tariff structure offers superior performance compared to the maximum flow restriction tariff structure, as it provides more effective cooling at end-user sites. Detailed information on these and other tariff structures is available in [PERSON] et al. (2016). Figure 15: Supply–return temperature difference (\(\Delta\)T) as measured for two cases with different tariff structures for their heat consumption, with VFM referring to the ‘Volumetric Flow Meters’ and MFR to the ‘maximum flow restriction’ and the design temperature scheme being 80/40 \({}^{\circ}\)C for a design outdoor temperature of \(-\)15 \({}^{\circ}\)C, reproduced partially from the source data shown in [PERSON] and [PERSON] (2016). [PERSON] et al. [129] highlight a limitation of conventional heat meters, noting that they lack the capability to assess cooling provided by consumers' heating units. This deficiency poses a risk, particularly when a consumer site is equipped with inadequately sized heating units, which may lead to exceptionally high flow rates. * Motivation Tariff  
Many DH systems incentivize customers to reduce their return temperatures by implementing pricing schemes that offer bonuses for achieving lower return temperatures and/or impose penalties for exceeding specified thresholds. This approach, known as a'motivation tariff,' is also referred to as a 'cooling tariff' or 'incentive tariff'. The Roskilde DH system, which supplies heat to 6500 customers, implements a motivational tariff, as detailed by VEKS [132]. The implementation of this tariff involved several steps:  
1. Determination of Reference Levels: The reference return temperature level was initially set by measuring the average return temperature of 28.5 \({}^{\circ}\)C during the 2001/2002 period. 2. Threshold Establishment: Based on these measurements, thresholds were established with a natural band of 5 \({}^{\circ}\)C. A bonus was awarded if the supply-return temperature difference exceeded 35 \({}^{\circ}\)C, while a penalty was imposed if it fell below 30 \({}^{\circ}\)C.
3. Consumer Engagement: Efforts were made to promote consumer awareness of this new tariff and to educate local heating and plumbing engineers about return temperature reduction techniques. 4. Initial Results: In the first year of implementation (2004), 1000 consumers received bonuses for meeting the desired return temperature criteria, while 4500 others received penalties. This incentive structure effectively motivated changes in consumer behavior. However, issues were identified, including poor cooling in some homes and faults with heating systems. Due to technological constraints that limited the ability to improve cooling, 48 consumers were exempted from the motivational tariff [132]. The Danish heat transmission company TVIS implemented an incentive tariff based on an anticipated annual savings of EUR 564,000 per degree Celsius reduction in return temperature (assuming an exchange rate of DKK/EUR = 0.106) in 2015.