Zeroth energy systems and district heat networks

[edit] The Zeroth Energy System: Connecting ambient loops and higher temperature district heat networks

The tightening timescales for reaching the 2050 net-zero carbon target require us to accelerate our efforts at the decarbonisation of heat. Ambient network systems, such as the Zeroth Energy System by Glen Dimplex Heating & Ventilation (GDHV), are being increasingly specified for multi-occupancy developments due to their high efficiency and capability to reduce a building’s CO2 emissions. This raises the questions: can the Zeroth Energy System be specified in a district heating priority area, and can it connect to the district heating network?

The Zeroth Energy System has been successfully installed in developments across the UK, both within and outside Greater London. One of the first installations under the GLA was the Church Road development by Galliard Homes. Along with projects such as Harbour Lofts in Poole developed by Acorn Properties and The Factory by Dundonald Church in London, it has been shown that ambient networks can help achieve compliance for complex projects and deliver high energy efficiency for a variety of building types. The Zeroth Energy System has now been specified for a large number of diverse projects across the UK that are either completed or currently under construction.

It follows that combining the benefits of ambient networks and those of district heating could offer efficiency improvements to many residential developments. To answer the questions of connecting the Zeroth Energy System into district heating networks and the benefits of such a connection, we should have a look at the methodology behind both technologies first.

[edit] The rising popularity of district heating networks

Heat networks are not a new concept. Modern third generation district heating networks have been deployed in Scandinavia for over half a century and their benefits for occupiers, developers and the environment have been well documented.

In response to climate change, the UK Government and many local authorities have shown support for increasing the use of heat networks, especially in high density areas. For example, London has been very vocal with plans to deliver 25% of its energy through large-scale heat transmission networks as a way to reduce carbon emissions and support a low carbon economy. Behind this support of large-scale networks is the wide range of benefits they can offer: The use of diverse fuel sources, utilisation of energy from waste heat, help with balancing energy distribution and delivery of cost-effective low carbon heat led to reduced energy bills, local economy growth and a flexible and stable energy system.

There is however a common misconception that a high temperature heat network must (at building level) be paired with a high temperature communal heating system. This is simply not the case as the system operating temperature can be adjusted as we will discuss later. Importantly, the major drawback of adopting traditional high temperature communal heating technologies in modern buildings with increasingly thermally efficient building envelopes is the heat loss that result in reduced efficiency.

Heat loss factors are not only indicators of system efficiency, they also directly impact the comfort levels of the occupants. In a modern, thermally efficient building, heat loss from the distribution pipework can cause overheating of service risers, corridors and apartments. .

[edit] The Zeroth Energy System and the efficiency of the ambient loop

The Zeroth Energy System is a low carbon solution designed with cooperation and feedback from construction industry experts and the BRE to address the challenges of distribution heat loss by using heat pump technology whilst aligning with compliance. The network of in-apartment water-to-water heat pumps is connected to an ambient loop operating at 25°C and can provide heating and hot water or heating, cooling and hot water using the same infrastructure without the need for a refrigerant.

The thermal energy can come from a renewable central plant, for example, air-source heat pumps, including those from a district heat network. The unvented 172l cylinder within each unit can provide hot water up to 60°C and, if comfort cooling is required, the system can transfer the waste energy from the heating process. Conversely, the waste energy from the cooling process can be transferred to the water cylinder to provide the thermal energy for hot water delivery.

Modelling in SAP 2012 shows that the efficiency of the system, when used with an air source heat pump, reaches 300% with a heat loss reduction of 90% compared to traditional high-temperature systems.

[edit] Connecting to district heating network

If you would like to benefit from a communal ambient loop but are wondering if this could connect to a higher temperature district heat network – then the answer is simple: yes.

Hydronic design connection to a district heating network can be achieved without major alteration to the system infrastructure. A spur would be required from the network into the building plant room. This would be connected to a plate heat exchanger to blend the temperature down to circa 25-40OC where it would be stored in a buffer. This would be blended again into the building’s ambient loop at 25OC to feed each apartment. In principle, the ASHP we so often see specified with Zeroth Energy Systems would be replaced with a spur to the district heat network.

Although the Zeroth Energy System is a relatively new solution, the technology is already up and running. There are currently over 120 projects in various stages of construction that are considering the Zeroth Energy System, albeit a large percentage do not require a connection to a district heating network, but they do utilise an ASHP as a central plant.

The consequence of replacing traditional high temperature systems that can suffer drops of efficiency to as low as 33% though distribution heat loss with an ambient loop communal system is a reduction of heat loss by 90% in a building. This leads to healthier buildings and increased energy efficiency. Connecting an ambient network such as the Zeroth Energy System into a district heating network also unlocks all the additional benefits such networks have to offer. This gives us the freedom to build well designed, comfortable and healthy buildings for the future.

To find out more information on the Zeroth Energy System or to discuss how your project could benefit from an ambient loop system, please contact our team of specialists.

--Glen Dimplex Heating & Ventilation 16:58, 09 Aug 2021 (BST)