CASE STUDY | THE HOUSE AT CORNELL TECH End users: modelled v actual operation The House is using 30% less energy than predicted in the as-built ASHRAE 90.1 model and in benchmark data for New York buildings of more than 200,000ft2 5.0 4.5 4.0 3.5 Site kBTU/SF 3.0 2.5 2.0 1.5 1.0 0.5 - Sept Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug 18 18 18 18 19 19 19 19 19 19 19 19 The House monthly PHPP modelled consumption Residents of The House are mainly one-year Masters students 5.0 4.5 4.0 Site kBTU/SF 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Sept Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug 18 18 18 18 19 19 19 19 19 19 19 19 The House monthly actual energy consumption 2018-19 5.0 4.5 4.0 Site kBTU/SF 3.5 3.0 2.5 2.0 1.5 1.0 0.5 - Sept Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug 18 18 18 18 19 19 19 19 19 19 19 19 The House monthly ASHRAE modelled consumption Key DHW gas Central areas heating and cooling Apartments heating and cooling Common areas Apartment electricity occupants to control the temperature of spaces individually was very important to the developers, explains Janiski. Before opting for the air-cooled VRF solution, Buro Happold assessed the viability of numerous heating and cooling systems based on 17 criteria, including: energy efficiency; space requirements; noise; thermal comfort; individual controllability; the ability to bill occupants based on individual energy use; and, of course, capital cost. The system alternatives considered included water source heat pumps and water-cooled VRF. The air-cooled VRF was more costeffective from a capital cost point of view, and it offered the ability for individual fan units in every living room and bedroom, Janiski says. The VRF outdoor units housed on the mechanical balconies are configured in an every other sequence, serving two residential floors at a time. One unit serves two floors of north-facing apartments, while the unit on the floor above serves the more tightly packed south-facing apartments on the same floors. To zone based on solar orientation and, therefore, similar amounts of heat gain or loss over the course of a day, and from season to season, it made more sense to have one unit serve two floors of apartments on the north and east, and another serve two floors on the south and west, Janiski explains. The system gives occupants a limited range of settings for the minimum and maximum temperature of their apartments, which, Janiski says, are set in line with Passivhaus criteria. Although residents can vary the temperature of their apartment, its fresh air supply and exhaust air rates are fixed. As with all Passivhaus schemes, filtered outside air is supplied to living rooms and bedrooms, while dirty air is extracted from bathrooms and kitchens. Unusually for a Passivhaus scheme, rather than use individual apartment units, all 365 apartments are ventilated by two rooftop energy recovery ventilator (ERV) units otherwise known as mechanical ventilation with heat recovery (MVHR) units. (See panel, Centralised ventilation). The House at Cornell Tech was certified by the Passivhaus Institute in September 2017. The Passive House Planning Package (PHPP) model achieved a primary energy demand of 120kWh.m-2 per year for heating, domestic hot water, household electricity and auxiliary electricity. At a PHPP-modelled energy use intensity (EUI) of 120kWh.m-2 per year, 20 April 2021 www.cibsejournal.com CIBSE April 21 pp18-22 House at Cornell Tech.indd 20 26/03/2021 17:26