This thesis investigated where and how critical heat customers should be addressed to lower district heating supply temperatures. It finds that critical heat customer initiatives should be prioritized where the local heat supply systems have a high variable heat prices, large production share covered by heat pumps, multiple heat production units, and low temperature benefitting technologies where fuel, taxes, operation and maintenance costs are high. It finds the best payback period for large heat customers that are about to renovate and choose an energy renovation supplied by a HP system. The worst payback period is found for small heat customers choosing a heating system design solution, and who is situated in a distribution grid supplied by a flue-gas condensing wood chip boiler. Generally, the business case is great across the different types of heat supply systems, but to harvest benefits and make critical heat customers invest, knowledge and actor network initiatives are needed. Three critical heat customer strategies to lower DH supply temperatures exist:
1. Address poor performing customers in distribution grids of hydronic bottlenecks
2. Address customers that cannot obtain thermal comfort at lower supply temperatures
3. Address customers that cannot ensure legionella safe domestic hot water
The findings indicate that the first strategy requires the least to execute. Actor-alignment may be achieved by the installation of a flow limiter because it allows the plumber to deliver a better service, because customers will request it. The second strategy may be more extensive because it requires the critical customer to energy renovate or increase the heating power of heat emitters. It requires persistent dialogue and outreaching, impartial and free consultancy to convince heat customers that it is worth the effort, and to provide them with knowledge and comfort to invest in improvements. Municipalities may be an obvious partner due to its’ expertise in participation process and the legitimacy they can add to the strategy. The third strategy may involve the implementation of more radical new technologies for large heat customers to ensure legionella safe DHW. Consequently, this strategy also requires persistent dialogue, and to a larger extent a demonstration that new techniques are adequate for the critical heat customer. Partnering with product developers may also enhance results from such strategy, due to their expertise in making the radical new technique work as intended.