KJ Tait

23 St Andrew Square, Edinburgh

First Sentier Investments

23 St Andrew Square is a single tenant occupied office building. Located in the Edinburgh New Town.  It is heated via fan coil units supplied from boilers and a chiller.  A supply air handling unit distributes tempered air to the office areas.


KJ Tait were instructed to investigate replacing the gas fired boiler with a low temperature heat pump and provide a pathway for the building to achieve Net Zero Carbon.



What we did


We conducted a site visit to investigate the current installations, review the building management systems and gather O&M information.  A full review of the current utility billing was carried out and benchmarked against typical and best practice office buildings along with the UKGBC benchmarks to 2050.


An IES model was built with fabric information used from the time of construction of the front façade and office extension at the rear of the building.  We then used IES Apache HVAC to create an accurate representation of the HVAC system including flow rates, control, off coil temperatures and operational profile.  The results from this model were compared against the actual gas consumption to evaluate the accuracy of the modelling.


From this baseline, we modelled differing scenarios to understand the potential reductions in energy usage along with an assessment of the comfort levels.



Added Value


The advanced modelling using Apache HVAC has allowed us to confidently assess the energy reductions that could be achieved for each initiative we have recommended.


Whilst it was suspected that replacing the boiler with a low temperature heat pump would be feasible, we now have confidence that the reduction in the flow and return temperature difference would not affect comfort levels significantly.





We have documented an investment grade report that recommends:

  • Replacing the boilers with a low temperature heat pump
  • Implementing fan coil modulation
  • Reduction in setpoints and ventilation run times
  • Replace AHU motor
  • Install PV


These measures would allow the building to reduce its carbon consumption by 45% and crucially could allow the building to comply with Net Zero Carbon in-use requirements as described within the UK Green Buildings Council guidance.