COOL DH will demonstrate high efficient District Heating networks and solutions using a number of innovations. Each innovation is presented in the following sections under demand, distribution and supply.
On the demand side we find end consumers of DH.
Local integration of renewable energy sources
COOL DH will work on solutions for preparation of DHW by preheating with LTDH and local supplementary heating with renewable energy on a substation level. The basic overall system is illustrated below. However, the source of heat for the heat pump varies and can come from cooling of exhaust air, recovery from wastewater, cooling of PVT (Photovoltaic Thermal) energy absorber etc. Different alternatives will be studied and evaluated before deciding what systems to demonstrate in the actual multifamily buildings.
COOL DH will also investigate and advice on the use of various substation solutions for single-family housing units. It will also find system solutions for multifamily houses and tertiary buildings like offices and institutions.
Reduction of energy demand for domestic water
Today, the energy for domestic water comes from heat pumps or electrical heating for temperature topping that could have been used elsewhere. Therefore, COOL DH will investigate if heat driven appliances such as washing machines and dishwashers can compensate for the additional electricity demand for temperature topping. The saving potentials in energy and costs will be evaluated, as well as the feasibility.
Too high return temperature
The LTDH system is monitored by direct connection to the consumers heat meters. This can be used to monitor heat losses in pipes, map consumption pattern and diagnose optimisation potential etcetera. However, today’s meter may not have an optimal resolution and sampling time for analysing the system performance in detail for short periods. COOL DH will investigate what is needed for sufficient evaluation of the system and how to read and process the data to be used for return temperature optimisation.
Solutions for avoiding risk of legionella
The challenge of LTDH is the temperatures needed for production of Domestic Hot Water (DHW). Lower temperature increases the risk of legionella and with today’s standards the heat limit is above 50-55oC for circulation water. 55oC is a legislative demand in Sweden.
However, several reports discuss this topic and in some countries 45oC is now allowed for plug flow installations with small volumes, that is when substations or micro heat exchangers are used. Another method is to heat the water to 45oC and sterilise it. A study on the legislative rules for Sweden, Denmark, and Germany etc. will be conducted and made public. The study will also evaluate different solutions on how to avoid legionella (for example micro electrolysis, UV treatment, use of substations in dwellings etc.).The report and will form the basis for solutions that will lead to implementation further on in the project.
New design concepts for optimisation of LTDH distribution systems
Traditionally, the DH-systems are oversized with a large safety margin, causing high system losses between 17% up to 35 % where energy density is low. About half of the heat loss is in the connection lines of the consumers. By hydraulic optimisation and decentral buffers the pipe dimensions and thereby the heat losses can be reduced, but the pumping energy and operation pressure of the system raise. COOL DH will use thermal and hydraulic simulation (using TERMIS and NETSIM) on actual pipes with a potential improvement of 50% reduction in heat losses. The system and its parameters will be optimised and presented to show the benefits.
New pipe components for LTDH distribution systems underground
Traditional pipes are made of steel for big dimensions and alu pex for smaller than diameter of 80 mm. These pipes are normally designed for 6 bar(o), 85 oC-110 oC in a 30 years lifespan. With the goal to reduce heat loss with 50%, COOL DH will introduce pipes which are not available on the market presently i.e. flexible multilayer polymer for 16 bar(o), 62 oC, 30 years.
5-10 prototypes of pipes will be pressure tested and certified, preparing them to be introduced in the demonstration part of COOL DH project.
Further, COOL DH will evaluate connection of pipes with a new improved type of push coupling of pipes. The aim is to introduce push fittings for underground LTDH pipes in smaller dimensions which would save much installation time. Today this technology is only used for indoor plastic pipes for HVAC. The new pipe connection types will be tested in laboratory.
New multimedia pipe types for LTDH distribution systems
The COOL DH project will innovate on the use of multimedia pipes i.e. pipes that carry different media and/or media at different temperature levels, as well as minimising pipe losses to zero or even negative. This is achieved by including a pipe that collects the heat loss and heat from the ground. The heat will then be returned to the inner pipe, using a heat pump.
New high efficient pipe types for internal distribution in buildings
Distribution losses are not limited to underground DH pipes but are also found in and between buildings or building sections with up to 15 % of the total energy need for energy renovated or new low energy houses. Pre-investigations indicates that this loss can be reduced by 50-65 % with better pipe layout and use of PUR insulated pre-fab DH pipes inside buildings. COOL DH will innovate the use of fire safe cuffs for pipe penetrations of building components and new ways of branching of pipes will be added.
Optimising cascade couplings for optimal use of low-temperature sources
COOL DH will study and innovate on optimal connections principles and controls of heat pumps/coolers to the LTDH system for both Lund and Høje-Taastrup.
Development of short time and seasonal energy storage in Høje-Taastrup
During the summer, the peak load for district cooling will benefit from having cold wells in an ATES (Aquifer Thermal Energy Storage) buffer to draw from. During warm summer periods, the need of the LTDH system will be low. Surplus heat is therefore abundant and can be stored in the warm wells of the ATES system.
When a ATES system is available, heat pumps can extract the heat when needed and supply it to the LTDH system and regenerate the cold wells for supply of district cooling. The heat pump can be controlled via price signals and/or weather forecasts/weather data, producing heat when wind/solar is abundant, allowing for a greater overall portion of renewables in the electricity grid as well. Innovative ways of using such heat pumps in will be studied in Høje-Taastrup.
If the ATES cannot be realised due to water interests or hydrogeological conditions a borehole energy storage system will be considered.
Added values of LTDH systems
Surplus low-grade fossil free heat at low cost can sometimes be used for purposes that are normally not used. Examples are snow clearance and improvements of conditions for soft transport i.e. pedestrian and cyclists. COOL DH will study solutions for:
- Pre-drying of new buildings. LTDH grid allows for early establishment and reduction of heating cost from first year of operation.
- Ice-free solutions for ground/squares/roads (can also be used in reverse during summertime as solar collectors).
- Green houses for urban farming and prolonging the growth period of trees and grassed areas by heat from return temperature in spring and fall.