Lowther Primary School, Barnes, London — removal of the existing gas boiler installation and replacement with an air source heat pump, complete replacement of the heating distribution and building management system, and upgrades to the school’s incoming electrical supplies. Delivered as decarbonisation works for Richmond and Wandsworth Council over twelve weeks.
The heat pump is the smallest part of the job
Decarbonising a school’s heating is usually described as a heat pump installation. In practice the heat pump is one line in a much longer scope, and at Lowther it was the electrical and distribution work around it that determined the twelve-week programme.
Taking gas plant out and putting a heat pump in moves the building’s heating demand onto its electrical supply. That supply then has to be capable of carrying it. At Lowther the incoming electrical supplies were upgraded, which meant trenching and cable ducting across the site, backfilling and making good afterwards, and sub-metering installed on the new supplies.
Distribution and emitters
Heat pumps deliver heat at lower flow temperatures than the gas boilers they replace. A distribution system and radiators sized for a boiler will not usually deliver the same room temperatures when the flow temperature drops, which is the most common reason a heat pump retrofit disappoints in use.
At Lowther the heating distribution was replaced completely, including all new radiators, so the emitters and pipework were matched to the new heat source rather than inherited from the old one.
Controls
The building management system was replaced in full and Trend IQ4 controls were installed, with a touchscreen interface for ease of day-to-day use and maintenance. The new system provides zonal control across the school.
Zoning matters more with a heat pump than with a boiler. A heat pump runs most efficiently when it operates steadily at a low flow temperature, so the ability to control where and when heat is delivered has a direct effect on whether the installation performs as intended once the school is using it.
Siting and planning
The heat pump is a Trane unit, Range CONQUEST Model CXAX 45 SE LN. A concrete base was installed to site it, and an acoustic enclosure was supplied and installed for both aesthetic and planning permission reasons.
External plant on a school site in a residential area is rarely a purely technical decision. The enclosure was part of making the installation acceptable in its setting as well as controlling noise.
Scope of works
- Strip-out and disposal of the existing gas boiler arrangement
- Supply and installation of a Trane air source heat pump — Range CONQUEST Model CXAX 45 SE LN
- Concrete base installed for siting the heat pump unit
- Acoustic enclosure supplied and installed for aesthetic and planning permission reasons
- Complete replacement of the building management system
- Trend IQ4 controls installed with touchscreen for ease of use and maintenance
- Complete replacement of the heating distribution including all new radiators
- Upgrades to the incoming electrical supplies
- Trenching and cable ducting, backfilling and making good
- Sub-metering of supplies
What the project demonstrates
Lowther brought mechanical, electrical, controls and civils work together under one appointment. A project like this is difficult to run as separate packages, because the heat pump, the supply upgrade, the distribution and the control strategy each depend on decisions taken in the others.
It remains one of the clearest examples of ComGas working across low-carbon heating, building management systems and controls and commercial electrical installation on the same site, for a local authority client in the education sector.
