GREEN LEAF ENGINEERING

Fitzharry’s School, Abingdon 

As part of the PSDS Phase 3a schemes, Green Leaf Engineering were employed by Surveyors to Education to carry out the design, supply, installation, and commissioning of 0.99MW of primary heating plant at Fitzharry’s School, Abingdon.
As part of the PSDS Phase 3a schemes, Green Leaf Engineering were employed by Surveyors to Education to carry out the design, supply, installation, and commissioning of 0.99MW of primary heating plant at Fitzharry’s School, Abingdon.

INTRODUCTION 

he proposal consisted of the replacement of the existing gas fired boilers with air source heat pumps configured in a hybrid system with gas boiler backups. The scheme consisted of three plantrooms spread across the site each with individual requirements for LTHW, DHW and configurations of ASHP installations. Works commenced from our appointment in December 2022 and were completed in April 2023 including commissioning, client training and handover of site to the school. The below case study details the technical requirements on site, processes and involvement from Green Leaf and challenges faced with solutions proposed by us as the MEP Contractor. 

SCOPE OF WORKS 

Block A The existing LTHW Boiler in conjunction with domestic boiler to generate local LTHW to serve the DHW cylinders were to be isolated, stripped out and replaced with 5 No ASHPs capable of delivering 400Kw combined thermal load. In conjunction with this a new primary buffer vessel and DHW cylinder were installed with the necessary circulation and shunt pumps. To cater for the revised electrical loading, a new MSB Incoming board and Section board for ASHPs was installed within the plantroom, including interconnecting LV Cabling. To control the new installation a new BMS panel was installed, including control of the ASHPS, pumps, DHW cylinder, and existing gas detection and control within the plantroom. As the ASHPs were to be cited within the plantroom louvre design and installation was undertaken to ensure adequate air movement is achievable. 

Block D+E The existing LTHW Boiler in conjunction with domestic boiler to generate local LTHW to serve the DHW cylinders were isolated, stripped out and replaced with 4 No ASHPs capable of delivering 300Kw combined thermal load. In conjunction with this a new primary buffer vessel and DHW cylinder were installed with the necessary circulation and shunt pumps. To cater for the revised electrical loading a new MSB incoming board and Section board for ASHPs was installed within the plantroom, including interconnecting LV Cabling. To control the new installation a new BMS panel was provided, including control of the ASHPS, pumps, DHW cylinder, and existing gas detection and control within the plantroom. As the ASHPs were to be cited within the plantroom, louvre design and installation were undertaken to ensure adequate air movement is achievable.  

Block G The existing LTHW Boiler in conjunction with domestic boiler to generate local LTHW to serve the DHW cylinders were isolated, stripped out and replaced with 4 No ASHPs capable of delivering 150Kw combined thermal load. In conjunction with this a new primary buffer vessel and DHW cylinder were installed with the necessary circulation and shunt pumps. To cater for the revised electrical loading a new MSB incoming board and section board for ASHPs was installed within the plantroom, including interconnecting LV Cabling. To control the new installation a new BMS panel was provided including control of the ASHPS, pumps, DHW cylinder, and existing gas detection and control within the plantroom. 

TECHNICAL SECTION

The initial design pack issued identified that three blocks, West Block, Science Block and Main Block could be reconfigured to include AHSP with Gas Boiler top up to achieve the desired heating loads. The loads required are detailed below. ·G Block (West) – 150Kw – LTHW only serving existing fan convectors ·D&E (Science Block & East) – 300Kw – LTHW and localized generation of DHW Via PHX and dedicated cylinder ·A Block – 400Kw – LTHW and localized generation of DHW Via PHX and dedicated cylinder. Through discussions with various suppliers in the heat pump market, it was determined that AIC Heating were best placed to provide a fully compliant system utilizing their 90Kw Aurax Heat Pump unit, in conjunction with their programmed Cascade controller, 1000L Buffer vessel and Silox Domestic Hot water cylinder. Data can be provided upon request. 

DETAILED DESIGN

As part of the project, Green Leaf were employed on a design and build basis to produce a RIBA Stage 4 Detailed MEP Design for this project. Green Leaf carried this out utilising both our inhouse design team in conjunction with our MEP design partner Wilson Grey. The design works that were required within Green Leaf’s scope to take it from the contract award at RIBA Stage 3 and project commencement at RIBA Stage 4 were as follows: Electrical LV Cable Sizing / LED lighting Calcs for replacement as VO / LV Distribution Design Mechanical System sizing and configuration including pipe & valve sizing / ASHP Selection and control philosophy / Buffer Vessel Sizing / Louvre Calcs and Design Construction Structural Report for builders works / MEP Plinth Design & Detail / Scaffolding Design / Temporary Works Designs including firestopping & trenching details.