VENTILATION A case study investigation2 was undertaken by Swegon and the University of Padua to investigate the potential operational benefit of applying DCV. The Engelsons building located in Falkenberg, Sweden, constructed in 2009, was used as the basis of an investigation to determine whether there were potential total operational benefits from the adoption of DCV compared with a simple CAV system. The 2,200m2, two-storey building was chosen for its mixed use, incorporating offices and retail with a packing area and a separate warehouse (which was outside of this study). The building was monitored, and a computer thermal model created and calibrated so that it provided a solid base for comparative system simulations. Unusually for such a building in Sweden, the building is not connected to district heating and is fully electric. Three sub-areas of the building ground floor retail area (439m2), ground floor packing area (514m2) and first floor open-plan office (481m2) were monitored for more than two years. The air handling unit (AHU) control system provided recorded measurements of temperature, relative humidity, pressures and airflows, and distributed logging devices were used to monitor the temperature and humidity of various spaces. Over the period of data Office zone: air temperature Temperature (oC) in higher overall airflow compared with alternative active measures of occupancy or building use, such as carbon dioxide (CO2) or volatile organic compound (VOC) levels. The supply air conditions. The principal operational benefits of varying air volumes comes from the reduction in fan power required to move the air through the distribution network. This can be further enhanced by optimising the supply air condition so that the total energy use, including that used in any terminal devices (which may be able to heat and/or cool), is maintained at a minimum. This requires that the control and feedback from room devices, zone controllers and centralised plant are all linked, so that the integrating controller can optimise the supply air condition The availability of global intelligence. Where systems are connected with internet-based resources, this can feasibly include whole system control and supervision that is influenced by information provided by for example weather and environmental forecasts, energy tariffing, and cloudbased, manufacturer-linked, conditionbasedmonitoring. 28 28 26 21 24 14 22 7 0 20 Thu Tue Sun Office measured at height 1.1m Sat Outdoor temperature Figure 2: Internal and external temperatures over a week in summer conditions shaded area is the recommended maximum temperature to EN 15251 collection, the monitored flowrates were reasonably consistent (aside from a step-change in supply airflow rates following some unreported systems changes to the packing area and some periods where data was lost). The area was served by what was fundamentally used as a CAV system, but with the facility for localboosted airflow, so effectively having the facility for VAV to increase the amount of air supplied though this was not used during the monitoring period. Fortunately, the period of monitoring was sufficiently long that a full years operational data could be extracted and linked up with the actual weather data for that same period. The investigating team selected weeks where the external temperatures were at the most extreme, to determine how well the systems controlled the spaces compared with the requirements of EN 15251,3 as shown in Figure 2 for the summer condition. The comfort conditions were evaluated using long period comfort (LPC) the cumulative hours over the period of each month that occupants have been outside of their comfort boundaries (as set by EN 15251). The method that was employed is explained in annex F method C of EN 15251, which employs predicted percentage dissatisfied (PPD)-weighted time, where the time during which the actual predicted mean vote (PMV) exceeds the comfort boundaries is weighted with a factor that is a function of the PPD. The guidance4 is that the PPD-weighted time of exceedance should not be greater than 150 hours per year. Long period comfort 3a) Office zone: WT warm/cool 500 400 Hours | 300 200 100 0 Jan Feb Mar Apr May Jun Annual W cool = 2,007 Annual W warm = 0 Jul Aug Sep WT warm Oct Nov Dec WT cool 3b) Retail zone: WT warm/cool 500 400 Hours CPD PROGRAMME 300 200 100 0 Jan Feb Mar Apr May Annual W cool = 0 Annual W warm = 780 Jun Jul Aug WT warm Sep Oct Nov Dec WT cool Figure 3: Monthly PPD-weighted comfort hours based on assumed level of activity and clo value synthesised from the running mean outdoor temperature a) office area b) retail area 32 June 2019 www.cibsejournal.com CIBSE Jun19 pp31-34 CPD 148 Supp v2.indd 32 24/05/2019 14:55