The use of heat pumps in district heating systems

Joe Grice

Energy capital projects manager

24/11/2015

Why Decentralised Energy

Heat Networks

• Green gas...

• Urban Waste Heat

• CHP & Heat Pumps

Offers a long term approach to heating for our residents giving flexibility of heat source and providing:

Reduced heating costs

A long-term flexible and expandable solution

Reliable and secure energy supply

Efficiencies of scale

Look to move away from gas

Combined Heat and Power

CHP is typically sized to meet baseload demand

Generates heat and power simultaneously

Most cost effective to run when electricity is most expensive

Heat Pumps

Efficiency is heat source and heat sink dependent.

More efficient at higher temperatures for heating.

Closer the heat source is to the heat sink, the higher the efficiency

Electricity Units Consumed

Heat Units Extracted

1 3 – 5 +

Coefficient Of Performance (COP):

COP 8 ≈ Z Factor 8

District Heating the ‘Heat Interconnector’

Biogas

BiomassElectricity

HP

HP Waste Heat

Waste Heat

Homes Retail

Industry

Commercial Chilled Water

HP

The Network

Thermal Storage

Used to improve the viability of the district heating scheme by adding storage to the network

Can store large quantities of heat, with very low losses.

Further the flow temperature of storage is from the return temperature of the network, the greater the thermal energy stored

RETURN TEMPERATURE of network is of greatest importance

Why use heat pump

• Adds greater resilience to the network.

• Energy input to a heat pump is electricity which can be fed from the power generated by CHP engine

• More efficient to use for heating when ambient temperatures are high

• CHP better when ambient temperatures are lower as export prices for electricity tend to be higher

• Common in Norway where hydro generated electricity is much cheaper than in the UK

• Main barrier to expansion in UK is electricity price and capital cost

• Eligible for government support in the form of RHI

Network temperatures

• Heat pumps are more efficient at lower temperatures

• Consideration should be given at an early stage as retrofitting into existing network is complex and expensive

• Secondary networks are often standard 82c/71c flow and return systems

• This can be relatively easily achieved at new build stage but existing buildings looking to connect may need to be incentivised

• Lower flow and return temperatures also reduce losses through the network

• An allowance would be required for larger distribution pipework

Operating Temperatures

High Flow Temperature

High Return Temperature•Plant runs inefficiently•Plant ‘trips’ off•Plant fails

Increased H&S risk

Increases heat loss – reduces system efficiency

Increases capital cost

Can increase return water temperatures – especially in oversized systems

Return Temperatures

Return TemperatureMore important than flow temperature

• Low temperature heat emitters

• Plate based calorifiers/DHW generation NOT coils

• Correct energy estimations based on realistic assumptions NOT peak demand. Part L is not appropriate – CIBSE TM 54 energy model recommended.

• High quality pumps – multiple pump design – pressure controlled

• Temperature controlled Bypasses

Electrical Demand/Supply Mismatch

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0 500 1000 1500 2000 2500

Elec

tric

ity

dem

and

and

and

supp

ly (

MW

)

5 minute periods

Electricity data for 19th May 2014 to 25th May 2014

demand

wind

nuclear

wind+nuc

High CO2 Electricity

Low CO2 Electricity

Credit: Paul Woods @ AECOM

District Heating Network Response

High CO2

Low CO2

-0.5 MWe / 2.5 MWth

2.5 MWElectrical

Swing

+2 MWe / 2.5 MWth

District Heating Network Response

High CO2

Low CO2

+2 GWe / 2.5 GWth

-0.5 GWe / 2.5 GWth

2.5 GWElectrical

Swing

Islington Celsius ProjectBunhill Phase 2 – Capturing heat

What is Bunhill Heat and Power?

A 1.9MW CHP plant based in Central Street that generates heat and electricity.

It provides heat to:

720 council homes 162 private homes 2 leisure centres

Electricity generated is sold the national grid

Phase will be a second energy centre with 2 x 350kW CHP engines and 1MW heat pump.

- Additional 800 council homes - Additional commercial buildings

• To demonstrate innovative solutions to the technical challenges of using low temperature heat to supply heat to new and existing homes.

• To connect a further 500 existing council homes and more new homes: Reducing energy costs by at least 10% to connected

residents to tackle fuel poverty Reduce carbon emissions Improving the security of heat supply

• To help London develop a replicable vision for how to evolve into a truly energy-smart city.

• To demonstrate and to promote roll-out of Smart District Heating through-out Europe and support 50 new cities by 2016 & another 100 cities by 2026.

Bunhill extension objectives

Development – How we got here

• Policies and guidance

– Well developed

– Council and member commitment

– Officer understanding

• Communication

– Consultation

• Information & Knowledge

– Spacial opportunities

– Strategic opportunities

– Best Practice

District Heating and Electrical Networks

The heat pump

• 1MW thermal output heat pump• Electrical input of 345 kW (Met by CHP engine)• Coil located within London Underground shaft as

ambient temperatures are higher• Ammonia refrigerant selected for highest COP

possible operation at higher temperatures• Ammonia is toxic and a fire risk. Safety features need

to be engineered into design

Ground and water source heat pumps

• Higher efficiency that air-source heat pumps• More complex and expensive to install that

air-source heat pumps• Very expensive and complex to retrofit into

existing networks• Can be integrated into new development and

could possible supply a district heating scheme

Conclusions

• CHP and Heat pumps are complementary technologies

• Heat Pumps with a COP ~ 8 are competitive with CHP

• It is easy and cheap to store large quantities of heat

• District heating is a technology agnostic energy distributor

• District heating facilitates the efficient utilisation and sharing of diverse energy sources including waste heat

• Waste heat includes conventional cooling plant

• In combination, these technologies facilitate the use and balancing of low carbon heating, cooling AND electrical demands