Case Study: New Linx Housing Trust
Newbuild Project of the Year 2013, H&V News Awards
Following the successful completion of a retrofit project in 225 of New Linx Housing Trust’s stock in 2008, in 2012 Kensa were approached by the social housing provider again to undertake a new build ground source heat pump project in 53 of its properties in Brackenborough Road, Lincolnshire.
The contract followed a successful large scale retrofit project between New Linx and Kensa in 225 of their housing stock.
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The project remit was to install new Kensa Compact High Temperature ground source heat pumps in external enclosures to each property, connected to a district heating scheme using a communal borehole ground array; the largest example of a communal ground array serving individual heat pumps. The programme of works was also the largest of its kind in 2012.
Space restrictions and billing issues do not favour plant room scale appliances in new build properties, so the use of a communal borehole ground array connected to individual heat pumps solved this issue and qualified the project for the commercial RHI Phase 1 tariff as it is deemed a district heating scheme. Typically, a separate ground array serves eight to ten properties in order that the installation could proceed in parallel with the different phases of the construction programme.
Besides securing access to the RHI, communal ground arrays provide other advantages. Conventional schemes featuring a single borehole per dwelling need to exaggerate the depth of each borehole to protect against exceptional demand at any single property. By contrast, a communal array allows the scheme designer to utilize a diversity factor, decreasing the average borehole depth per property. Project costs are also lower because drillers can enhance their productivity by providing a lesser quantity of deeper holes, which also enhances overall system efficiency.
Although somewhat counter-intuitive, the standard Kensa Compact low-energy Grundfos pump is able to circulate the heat transfer fluid around the communal array should a single property call for heat as the required flow rate to satisfy such a limited demand is extremely modest. When more properties require heat, additional pumps contribute to the task which ensures the flow rate is always adequate. As a result, there is no additional plant which requires any maintenance. Sophisticated meters have been installed which allow New Linx staff to drive past the development and obtain the meter readings which must be forwarded to Ofgem to trigger the RHI payments.
From a tenant standpoint, low temperature radiators mean the expected seasonal performance factor is sufficient to generate running cost savings compared to the use of a mains gas boiler.