The Facts
Client – Marks & Spencer
Location – Borehamwood Food Hall
Duration – 6 Weeks (Mixture of day and night working)
Completition – 01/12/2023
Sector – Retail / Commercial
Budget – £296,842.60
Objective – Replace legacy gas heating with high-efficiency, low-carbon AHU and heat pump system.
Constraints – Works carried out in a live food retail environment; no disruption to customer operations or food-safe conditions.
The Challenge
This air source heat pump installation at M&S Borehamwood forms part of the retailer’s Plan A strategy to improve energy efficiency and reduce carbon emissions across its estate.. At Borehamwood, the 1,300 sqm food hall — including an 800 sqm open-plan shop floor with vaulted ceiling — was previously served by a failing Reznor RPVE 2046 direct gas-fired supply fan. It had supplementary electric fan coil units, destratification fans, AC cassettes, and local electric heaters. The legacy system was inefficient, underperforming and as the retail layout has changed over the years; only 3 out of 7 fridge isles had any heating in them. Overall, this led to high energy costs, inconsistent thermal comfort, and a poor carbon footprint. Some challenges to over come on site were all the back of house ceilings were to be removed to all safe access. There were some external condensers to relocate to allow the space to accept the new packaged AHU/ASHP. The ground was on a significant slope and wasn’t suitable to be shimmed level.
The Solution
We designed and installed a future-ready, fully electric HVAC solution built around a natural refrigerant air source heat pump with integrated air handling. With a full new ductwork system delivered tempered air to the right zones.
- High-Efficiency Air Handling & Heating
- Clade Spruce 128kW Combined AHU / Heat Pump
- CO₂ refrigerant (GWP = 1) for ultra-low environmental impact
- Heat recovery from return air to reduce demand
- Variable speed inverter compressor for thermodynamic stability and seasonal efficiency
- Air off temperature up to 30°C with an airflow of 8m³/sec
- Air Distribution Strategy
- Back-of-House: 900mm² galvanised insulated ductwork
- Shop Floor: 1,100mm circular exposed fabric sock duct system
- Branch ducts run between fridge packs with perforations for even air distribution
- Mounted at 4.4m height to complement open vaulted ceiling
- Smart Integration
- Fully integrated into the existing Building Management System (BMS)
- Remote monitored and controlled via RDM interface
- Safety Built in
- Maintenance walkways installed with hand rail and lighting.
- Palisade fence and gate orientation altered for safer access.
- External condensers relocated to a safe location with drip trays installed to manage the condensate.
The Result
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This air source heat pump installation eliminated 121.5 tonnes of CO₂ annually while improving thermal comfort and system efficiency across the site (based on legacy gas consumption of 664,300 kWh per annum)
- Site now operates using natural refrigerant (CO₂) with GWP of 1
- Significantly improved thermal comfort and coverage, including consistent heat between fridge packs
- Elimination of gas infrastructure, standing charges, and boiler servicing
- Simplified system with lower maintenance burden and full BMS oversight
- Fully aligned with M&S’s Plan A sustainability goals
A Bold Step Toward Net Zero
By replacing a failing, over complicated heating strategy which used a gas-fired unit, we’ve enabled M&S Borehamwood to drastically cut operational emissions, improve in-store comfort, and future-proof the asset against rising energy costs and tighter sustainability regulations.