Design and Technologies
On this page, we describe some of the decisions that were taken in response to the QB2 design criteria. We will also outline the key technologies that makes the Cube so energy efficient and, hence, environmentally friendly.
The Cube is designed to generate all the energy it needs, averaged over the year. In its "home" configuration, it is equipped with two Mitsubishi PVP 148 solar modules, each around 11m2 in area and each with a peak power output of 1.48kW. These were installed by Peter Morgan from Morgans Electrical, as was the remainder of the electrical system. Peak power is only produced from the PV panels in strong sunlight, but data show that we can expect around 280W in electrical power averaged over the year. This gives us 6.8 KWh a day or 2,480 kWh per year. If the Cube were registered with the UK Government's Feed-in Tariff, then this energy production would raise around £400 per year, tax-free, guaranteed and index-linked for 25 years.
Energy Use for Heating and Electrics
QB2 is a well insulated building, constructed from a bespoke post-and-beam system developed by us with our partner Bolton Buildings. Our prototype QB2 is clad on the outside by FSC-certified English Sweet Chestnut from Vincent Timber and, on the inside, by FSC-certified birch plywood. There is 140mm of PIR insulation in the walls, 120mm in the floor and the ceiling, and with Nordan's NTech triple-glazed Passivhaus windows and door. Heat loss (including 2 air changes per hour) is around 30W per degree C of temperature difference between the outside and inside temperatures. Given an estimated 2020 degree-days of heating requirement per year, this would give 1450 kWh of heat loss over the year, or an average of 4 kWh/day. This space-heating demand will be met by an Ecodan Air-Source Heat Pump (ASHP) from Mitsubishi Electric, linked to a DeLonghi Climaveneta MHD30 fan coil supplied by ICS Heat Pumps.
The Ecodan ASHP will also meet the demand for hot water, stored in a 100-litre pressurized cylinder, designed by World Heat Ltd to fit under the shower area. Water use is minimized by the use of Hans Grohe low-flow, high-performance showers and taps, so we assume a demand for 100 litres of hot water per day, at a temperature of 40 degrees above mains water temperature. Heating the water will, therefore, require an additional 4.6kWh of heat per day, giving a total heat demand for water and space-heating of 8.6kWh. Assuming that the coefficient of performance of the heat pump is equal to 3 (this is the number of units of heat that can be generated in the Cube for each unit of electricity supplied), we will use 2.9kWh of electrical energy per day to meet this total heat demand, or 130W on average.
Electrical demand is estimated at around 150W on average, including energy for Homewatt's high efficiency LED lighting, a low-energy LED TV, an induction hob, a combination microwave oven, an A++ rated fridge, a Ventair heat recovery ventilator, a Berbel Firstline recirculating cooker hood, an A+++ washing machine, and a laptop computer.
Other environmentally friendly features
The Cube sits on Swift Miniplinth foundations that use much less concrete than would a traditional slab, are both reusable and recyclable, and leave no lasting imprint once removed. Similarly, the building is anchored to the ground using Spirafix Ground Anchors that each resist over a tonne of pull-out force, but that are removable by simple unscrewing.
The composting toilet was jointly developed with Andy Warren from Natsol Ltd, adapting their standard pedestal to the particular space demands of the Cube. The system separates urine from solid waste, the former mixing with the Cube's grey water and flowing to a soak-away (probably via a reed-bed), and the latter being composted.
The Cube has bespoke furniture, including two armchairs designed by Mike Page and Linden Davies and constructed from sustainably sourced wood by Ben Whistler Ltd. The upholstery uses a special fabric developed by Camira Fabrics, comprising 75% wool and 25% fibres derived from nettles. The mattress is made from natural latex with an organic cotton cover.
Finally, the roof is covered with an EPDM membrane.