District Heating & Cooling Networks

District Heating Design

Mindful of the need to control carbon emissions, the Mayor of London has produced a District Heating Manual for London. It states that:

The 83 page document, produced in collaboration with Arup, is recommended for its practical approach to district heating design.

Particularly instructive is the chapter on "Innovation and the future of district energy in London" which looks at "the future direction of the district energy industry, in particular with regard to 'fourth generation' district heat networks".

Some quotes from the chapter:

The interesting threads of thought running through these points have been synthesized into a radical new approach to the design of heat networks which is being implemented by the BEN Consortium at the London South Bank University: a heat sharing network.

District Heating Design avoiding Combustion

Energy Trilemma

There is an alternative to gas-based CHP district heating which is more effective in resolving each of the three facets of the Energy Trilemma. To avoid emitting CO2 from heating it is important to avoid combustion. This can be done with the electrification of heating and utilising:

These can all be achieved using ground source heat pumps, which can also concentrate heat.

Instead of an expensive central energy centre sending hot water through an expensive steel pipe network, a small diameter flexible plastic pipe network connects each building with water close to ground temperature. Each building employs a heat pump to extract heat if it needs heating, or reject heat if it needs cooling.

This radically simpler mechanism yields no carbon emissions on site – nor any other product of combustion – and allows for incremental expansion of the network at marginal cost. Each building is in control of its own costs and its own temperature controls.

The following table compares traditional gas-based heat networks with the heat sharing alternative:

Traditional Gas-Powered District Heating Heat Sharing Networks
High cost of insulated pipework Low temperature pipe network
No cooling without separate additional circuit Cooling from heat pumps
Large additional cost for cold circuit Separate cold circuit not required
High cost of central heat generation Low cost local heat pumps borne by tenants
High running costs of central heat generation Local heat pumps under tenants' control
Admin cost of metering, accounting, collecting revenues Tenants pay their own electric cost directly
Heat Sharing dividend
CHP systems emit CO2 and other noxious gases No on-site emissions at all
Can use waste heat
No heat recycling Provides Seasonal Thermal Energy Storage
Uncertainty of future heat demand Allows incremental expansion
Uncertainty of future heat sources
Legal cost of agreements to share capital costs Legal cost of agreements to share (lower) capital costs
Legal cost of agreements to share high running costs Low central running cost minimises risk
Legals need to meet changes of tenants during the scheme Fewer barriers to new tenants - low risk to existing tenants