We have a vision for Glasgow. This vision is for Glasgow to become the most sustainable city in Europe.
For us, the definition of sustainable growth in Glasgow is to find a solution that can meet the needs of a growing and progressive city, without sacrificing the fundamental social needs of its people and surroundings.
These three pillars of sustainability – the economic, environmental and social constraints are where we started in defining our project. We concentrated on what we believed was one of Glasgow’s biggest problems – social housing – and thought how we could turn it into an asset. In concentrating on making the social housing more sustainable, we could tackle all three constraints.
Social – the expensive running costs of high-rise buildings are a breeding ground for Fuel Poverty.
Environmental – Large stock means that significant carbon savings could be achieved
Economical – Investing in sustainable energy often saves money each. An important aspect of our work is to find out “economically-sound” ideas.
We started to look at variety of sustainable technologies – such as wind turbines, low-head hydro and solar PVs. All technically sound ideas, but we initially came up against some strong barriers.
These were low density supply solutions to a high density demand.
None of these looked to be cost-effective
The only solution we discovered had any potential was CHP – combined heat and power. CHP basically moves the power station closer to home, allowing the waste heat in the generation process to be used in the household – achieving higher overall energy efficiency.
We started to investigate the conventional way to design micro-CHP for the household. CHP is mostly treated as a heat-led solution – on the smallest scale, the largest micro-CHP producer – WhisperGen, produces a unit which is sized to replace a boiler for a large house.
Our analysis shows that this technique is very wasteful, as the space heating load varies dramatically throughout the year. A minimum payback period for installing this system in a high-rise building was found to be 14 years. See HERE for more information.
We concluded that the best way to reduce space heating bills is to not optimise a badly-designed CHP system, but to reduce the loads themselves. We undertook an analysis to quantify the impact of adding Insulation, Double Glazing, Draught Proofing the building and installing smart temperature control in the space. We discovered that the space heating load can reduce from 69% of the overall energy consumption to only 21%.
We also looked into ways to reduce the electrical energy consumption. By installing energy efficient bulbs, energy efficient appliances and by hang-drying clothes – a further 5% of the overall energy consumption can be reduced.
So… what about CHP? There still remains a significant heating load in the domestic household. Hot Water. 25% of domestic energy use in the UK is to produce hot water for your baths, showers and taps. From BREDEM modelling, the average person uses around 40l/day – which in our average occupancy level in Social housing of 1.5 people is around 3200l/day per highrise. The hot water demand does not vary seasonally.
The CHP is sized to only cover the baseload of the electrical demand, so it does not have to export electricity (at a fraction of the cost it will buy back from the grid) – so the CHP can run at maximum capacity all day and all year. This produces a constant level of heat, which can be put into the existing hot water tanks in each flat to buffer out supply and demand.
A minimum number of 80 flats should be added together on the Baxi Dachs 5.5kWe micro-CHP to achieve the baseload electricity. This CHP system does not waste as much heat, so actually achieves a slight deficit of 8% of hot water. This can be easily met with the existing immersion heater connections in the hot water tanks if necessary.
For the tenement block, we concluded that the WhisperGen as it was only 10% electrical efficient produces too much heat and therefore the system was not suited for the hot water load.
In the highrise, we can achieve a 63% reduction in energy consumption which corresponds to a 65% reduction in Carbon Emissions.
The capital investment for employing all the heating reduction techniques was estimated to be around £3500 and could achieve a payback in 4.9 years.
The capital investment for employing the CHP for hot water was estimated to be around £960 with a shorter payback of 3.7 years. A combined reduction and CHP system could cost £4350 and could be paid back in 4.6 years. This is far better than the equivalent cost of £4400 of installing a CHP for the central heating, but with the far less favourable payback period of 14 years.
Our vision for the future: with 15,000 households in high-rise in Glasgow – with an investment of £14.4 million, you could receive payback in only 3.7 years. And annual savings of £3.9 million. This saves around 19,300 tonnes carbon per year at a carbon investment total of £750/tonne.
© University of Strathclyde 2009
