HEAT NETWORKS | PLYMOUTH CITY CENTRE A Central energy centre. Heat pump and gas boilers B High-density residential HIU feeding direct DHW and space heating C Commercial/office space D Local air source cooling Figure 1: 4th generation district heating and cooling heat or cooling source or potentially for heat storage, says Selman. The wells being drilled by the contractor are the first step forward on the 5DHC scheme the system will use an abstraction well and recharge well to balance the ultra-low temperature headers. These will require an Environment Agency licence to abstract water, Selman says. Eventually, wed like to tie in the system with a marine water source heat pump as well, where the new network meets the waters edge. The plan is for a two-pipe network to link the developments to enable them to share energy; the warm pipe is expected to be at around 14oC roughly the temperature of the ground and the cold pipe at 6oC, so there is no need to insulate the pipes. The ultra-low temperature network will allow usually rejected energy to be recovered and shared within, as well as between, buildings that are heating and cooling, simultaneously reducing primary energy and increasing system efficiency, says Justin Etherington, associate director at BuroHappold Engineering. Depending on the results from the well excavation, surplus energy is expected to be stored in the ground to keep the system in balance. Building heat pumps Boreholes providing seasonal storage A Residential with direct space heating and DHW booster B Distributed heat pump plant rooms C Commercial/office space with direct/FCU space heating and point-of -use DHW booster D High-temperature cooling (chilled beams) Figure 2: 5th generation district heating and cooling still be available in two years time. There is a question about the existence of the RHI post 2021, without which the economics of the scheme may not stack up, warns Selman. Instead of using abandoned mine shafts, asin the Netherlands, the Plymouth scheme uses geology. We looked at the geology underneath Plymouth and found a thick belt of limestone that has a principal aquifer running through it with a significant flow of water from east to west that we could use as a Heat pumps within each building provide heating or cooling as required. This is a very neat solution that allows a building to connect with two pipes, from which you can satisfy both the heating and cooling demand, meaning a building doesnt need flues, gas connection, rooftop chillers or plant, Etherington says. In each building, the heat pump is connected to a thermal store. This enables the building to meet peak demand without the need to size the heat pumps accordingly. The storage also gives Plymouth City Council the ability to decouple loads from the system, so it could use the system in a dynamic demand response mode. You could use the heat pumps in communication with the power grid as part of a multi-vector response, for example, power prices spike between five and seven oclock, so you could manage the thermal store to avoid running the HPs at that time, says Etherington. It is early days for the 5DHC network at Plymouth. The HeatNet team is focused on identifying local opportunities to achieve a working installation of a smart thermal energy network in Plymouth. The hope is that the learning from this project can inform UK-wide guidance to encourage others to follow similar approaches. CJ T he project and the lessons for similar developments was presented at the 2019 CIBSE Technical Symposium by Phil Jones of Building Energy Solutions, who has been involved in the project, bit.ly/CJAug195DHC Read about the 5DHC balanced energy network at South Bank University Intranets for heat, May 2019, CIBSE Journal Commercial Heating Special, bit.ly/CJAug19BEN 3803,1*6(/(&7,216)25 38%/,&+($/7+(1*,1((56 6SHFLDOLVWLQZDVWHZDWHUDQGVHZDJHSXPSLQJ 5DSLGUHVSRQVHSXPSDGYLFHVHOHFWLRQVGDWDVKHHWV %HVWWHFKQLFDODQGFRPPHUFLDOSXPSVROXWLRQV ROXWLR &DOORXUH[SHULHQFHGWHDPWRVSHFLI\\RXUSXPSLQJVROXWLRQ )ORRU0RXQWHG/LIWLQJ6WDWLRQV 32:(5( %< ZZZSXPSWHFKQRORJ\FRXN N