BMS | CONTROLS OPTIMISATION BACK IN CONTROL The optimisation of HVAC controls for a Croydon office has reduced energy use by 28% over nine months, resulting in a 171,000 saving in operational energy costs. REsustains Annie Marston describes how CO2 was slashed for a minimal capital cost saved 171,000 in operational energy costs over the nine months (see Figure 1). Knollys and Stephenson House The building This multi-tenanted building is heated and cooled using the original variable air volume reheat system that has been adjusted over the years. The chiller and cooling towers have been decommissioned, and variable refrigerant flow (VRF) systems have been installed in individual offices to cool them in the summer. The building was using approximately 215kWh.m-2 (gas and electricity together) each year, which corresponds to emissions of 1,110tCO2 and an operational energy cost of around 26/m2. A data gateway was deployed in April 2022, and has been streaming to the REsustain platform since then. To make the most of the polled values and to fully understand the building, a full-calibrated dynamic thermal model of the building was created. This includes principal HVAC specifications and control patterns. The building geometry was modelled in DesignBuilder v7 and then transferred to the EnergyPlus v9.4 calculation engine. The internal gains were based on site visit information, and the annual pattern of occupancy, lighting and plug load in the spaces were taken from standard ASHRAE 9.7/m2 232 tCO2 65 kWhm-2 4,500 180k 160k 28% Energy use without control optimisations 3,500 2,500 2,000 1,500 140k 120k 100k Energy use with control optimisations 3,000 1,000 500 80k 60k 40k 20k 0k Aug-23 Jul-23 Jun-23 Apr-23 May-23 Mar-23 Jan-23 Feb-23 Dec-22 Nov-22 0 Oct-22 Total energy usage (MWh) 4,000 Operational cost-savings () A s concern grows over climate change and our ability to meet our environmental, social and governance targets, we often overlook our existing building stock. We tend to assume that improving this stock will be prohibitively expensive and disruptive. Without attention, there is a risk that these sites will become stranded assets (buildings that the owners will no longer be allowed to sell or rent). Frequently, it is assumed that once a building management system (BMS) has been installed or upgraded, the site will run efficiently. This is usually not the case, however. Often, these systems are not programmed correctly or are adjusted over time and rarely recalibrated as the building evolves. As part of the solution to making sure our buildings are fit for purpose five to 10 years down the line, we need to make the building truly smart, using automated continuous control optimisations with regular seasonal recalibration via the BMS. If we do, we can reduce the carbon emissions associated with each building, typically by 20-60%. This case study covers work done by REsustain with Feldberg Capital on Knollys and Stephenson House, a 17,600m2 (net lettable area) office building in Croydon, built in 1967. The continuous control optimisations were implemented from 1 October 2022, remotely via a gateway to the BMS. From October 2022 to July 2023, these improvements have provided 28% energy savings, avoided the need to emit 232tCO2 into the atmosphere, and Figure 1: Savings after nine months of optimisation 54 December 2023 www.cibsejournal.com CIBSE Dec 23 pp54-55 Opimising BMS.indd 54 24/11/2023 14:52