This approach will result in the progression of building designs towards being totally self-sufficient of energy/water requirements and towards a goal of zero energy buildings.
By using available ambient energy resources open to us and with a small upgrading of building cooling load, heating and electrical energy requirements of the building can be met by these resources, with the absolute minimum energy input required, provided by the addition of a base load chp gas engine or fuel cell installation. A choice of various fuels for fuel cells are practical and available for inclusion in the design.
The blueprint system choice shows a four-pipe active chilled beam installation with a minimum low velocity fresh air ventilation plant. However, this philosophy will also be applicable and function well with all air systems, displacement ventilation and chilled beams or cooled ceilings, and certain available low temperature selected underfloor heating systems.
The blueprint is for UK and overseas projects with daytime and night-time phase change heat storage charging with water and photovoltaic panels, together with external adiabatic fan assisted heat exchangers. External exchangers can also reject heat peaks when the collective energy cannot be usefully used or stored.
The following is a review of some of the various elements of the blueprint when considered together with the schematic.
With available UK phase change materials/eutectic solutions and French thermal energy storage vessel technology, the proposed phase change stores and temperatures shown are currently available to store heat energy with the phase change operating at their selected temperatures.
Like the steam turbine, the system is based on the Rankine power cycle but uses the advantages that an organic working fluid has at low temperatures. Properly selected organic fluids result in the use of smaller more efficient turbines, eliminate the need for superheaters and allow the application of sealed units. This is similar to refrigeration compressors, and requires little maintenance other than periodic cleaning of heat exchanger surfaces.
The working fluid is vaporised by waste heat in a vaporiser or boiler, which is selected for the waste heat stream. The pressurised vapour expands through a uniquely selected, organic vapour turbine which is direct coupled to a generator producing conditioned grid-synchronised electric power. The low pressure turbine exhaust is condensed in a surface type condenser and the condensed fluid is pumped to the vaporiser by the feed pump. However, due to low carnot cycle efficiency, electrical generation is limited to 5% of the available heat source.
Economic thermal upgrading of heat energy with a chiller from stores at 15/18°C to 30/35°C ensures a high coefficient of performance (6:1 and above). Optional external air (or ground source open loop) to warm water heat store upgrading is also shown as a possible addition to meet winter energy requirements.
These are shown as part of the blueprint to provide their contribution towards a building's energy use. For UK buildings unglazed water solar energy panels can show better paybacks than glazed panels. A typical photoelectric panel measuring 1·18 m by 0·53 m can produce a peak output of 75 W and around 70 kWh per year and can partly meet the building's electrical energy loads.
This ca be used to meet autumn, winter and spring process cooling requirements to provide water at 15°C. However, this will override to some extent the chiller upgrading of heat gains from the cold store to the warm store for heating and electrical energy generation. By keeping the heat store temperature differences low, and as close as possible to 20°C, the chiller coefficient of performance of the upgrading rises to 6:1 and above.
These are available with various options for choice of fuel. Heat recovery chp with fuel cells or gas engines with low-grade water temperatures is indicated on the blueprint.
It is common practice to use the plate heat exchanger to recover waste heat from exhaust air to provide either a base load or pre-heated supply air. In the summer months the outside air is at a higher temperature than the indoor air so cooling rather than heating is required. One method to achieve this is to spray water over the extract air plates of the heat exchanger where it is evaporated by the warm air. It indirectly cools the supply air at a constant absolute humidity. A direct expansion system or a desiccant wheel with solar or waste chp heat is also shown as a second stage dehumidification step if required.
Source
Building Sustainable Design
Postscript
John Dalley C Eng, MCIBSE is an engineer with Design Installation Service. He holds copyright on the blueprint overleaf. Contact him directly with comments or questions on 01242 533120 or e-mail jdalley@dis-ltd.co.uk
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