FREECOOL

About

Summary FREECOOL integrates a passive ventilation system with a low-energy cooling system to reduce the reliance on mechanical HVAC systems for thermal comfort in hot climates. FREECOOL ventilates a building, above the recommended ventilation rates of 10L/s/person, regardless of wind velocity and direction, whilst also reducing the temperature of the supply air. This is beneficial for occupant health and wellbeing regarding pollutant concentration, but also thermal comfort and energy demand of HVAC systems. FREECOOL minimises the use of mechanical systems in buildings by lowering the inlet air temperature by 12-15°C, reducing the demand placed on mechanical systems up to 60%. Project Status Development of FREECOOL has been funded from TRL 1-4 by QNRF and from TRL 4-8 by EPSRC IAA. The InnovateUK 4th Round Energy Catalyst grant will fund a full scale pilot study of FREECOOL, undertaken at the Shaikh Khalifa School, Abu Dhabi, to create the first passively ventilated and cooled school campus in the UAE. Twenty four passive cooling units will be installed at the school campus, and used to provide passive lower the incoming air temperature, thereby mitigating the demand placed on mechanical HVAC systems and reducing the energy costs. In partnership with the University of Sheffield’s Advanced Manufacturing Research Centre (AMRC), FREECOOL units will be designed to be market-ready for worldwide distribution with maximum efficiency, providing the lightest, strongest and most effective solution. Independent verification of the FREECOOL system will be undertaken by the BRE. The current project follows small scale pilot work completed in Ras-Al-Khaimah. A uni-direction FREECOOL unit was connected to a test room. Measurements taken from the pilot system showed that a temperature reduction of 11.54°C in the incoming air occurred in July when the outdoor air temperature was 40°C. Details of this work can be found in Appendix A of the supporting documents. Description FREECOOL is a passive ventilation system integrated with a low-energy cooling technology, designed to radically reduce the energy demand of mechanical air-conditioning systems, which can account for above 60% of demand during the cooling season, by lowering the supply air temperature in hot climates. Wind towers are a passive ventilation system that have been used for centuries in the Middle East and through modern development, been utilised more recently in other parts of the world. Using wind driven and buoyancy forces, air is supplied by the wind tower to a building with zero energy input. This provides ventilation to a building with no energy input. However, thermal comfort can only be achieved with this system when the outdoor climate conditions are favourable. When outdoor air temperature is above indoor air temperature, as is common in hot climates, air cannot be introduced as this would increase thermal discomfort. This limits application and operation of wind towers. FREECOOL uses heat pipe heat recovery devices integrated into the wind tower to provide cooling. Heat pipes are sealed tubes partially filled with a fluid used to transfer heat between fluid streams at different temperatures. Heat is transferred due to pressure changes in the pipes, as fluid evaporates and condenses at either end of the heat pipe. This is a passive process as no energy input is required to transfer heat. Cooling is provided to the incoming air as heat is transferred via the heat pipe arrangement from the incoming airstream to a small, insulated water tank attached to the top of the wind tower. This is non-potable water taken from sprinkler systems and is held at 19-22°C, providing a temperature differential with the outdoor air to provide cooling/pre-cooling. This water is periodically replaced, to be used as greywater, to maintain the temperature difference with the outdoor air, this is the sole process where energy input is required. A common problem associated with heat recovery technology integration with passive ventilation systems is the pressure drop caused to airflow moving across the device. This limits the volume of air introduced and so reduces ventilation supply rates. This has been overcome by FREECOOL due to optimised design and arrangement of the heat pipes. Field testing shows that adequate ventilation rates are still achieved by the FREECOOL system, as compared to a wind tower without cooling technology integration. This is the first passive cooling system to achieve this. Providing low energy cooling, through the use of a closed-loop heat pipe system, for incoming fresh air temperature reduction enables the use of wind tower passive ventilation systems to be used to introduce cooler air to occupied buildings. The lower temperature of the incoming air reduces the demand on mechanical air-conditioning systems as less cooling is required. This translates to lower costs for the building operator and lower greenhouse gas emissions for the environment. By reducing the reliance on mechanical HVAC systems smaller, more efficient systems can be specified to consumers and building operators furthering the cost savings. Innovative Aspect No current ventilation system, passive or mechanical, has the ability to supply the required ventilation rates and cool incoming air for as little energy as FREECOOL. A number of companies design, manufacture and commission passive systems. However, no system is capable of adequately affecting the temperature of the incoming air. This limits the use of these systems to times when conditions dictate, requiring mechanical HVAC systems to operate instead. This increases the energy demand compared to a passive system used year-round. Though mechanical HVAC systems are capable of altering the condition of incoming air for occupant thermal comfort, and have become more efficient, these systems require high energy input for operation. Mechanical HVAC systems are now commonly installed with heat recovery devices to limit the energy required for thermal comfort. However, these devices cause a high pressure drop on air flow, and so require additional fans to circulate the air. This can lead to an overall increase in energy demand if the energy required to circulate the air is greater than the energy saved by the heat recovery device. FREECOOL integrates passive ventilation with low-energy cooling technology. This innovate approach couples the delivery of supply air without energy requirements with heat pipes to condition incoming air. The heat pipe arrangement is designed to limit pressure drop on air flow, with maximum temperature change of incoming air. The innovation shown in this design has been proved following the granting of a number of patents, publications and funding relating to this work. Benefits FREECOOL provides a number of benefits over existing ventilation systems, both mechanical and passive. As a passive system, with no additional energy input for ventilation required, despite the ability to ventilate up to and above the guideline supply rates, FREECOOL has significant benefits over mechanical HVAC systems. Reduced energy demand is a cost advantage to building operators and managers as lower costs are required for operation. Further to this, energy reduction leads to reduced CO2 and other greenhouse gas emissions to the atmosphere. Given the high profile of climate change and steps required to mitigate this with reduced energy generation and lower emissions, the use of FREECOOL for ventilation is highly advantageous. A further benefit of passive ventilation provided by FREECOOL is the improved indoor air quality stemming from the supply of outdoor air compared to recirculated air by mechanical HVAC systems. Multiple studies have shown that a passive ventilation system that introduces fresh air directly from outdoor sources improves indoor air quality, reduces airborne pollutant concentration and improves occupant health, well-being and productivity. Despite the benefits that FREECOOL provides as a passive ventilation system, a number of other passive ventilation systems are currently available that provide the same advantages and benefits. The differentiator between these passive ventilation systems and FREECOOL, is the ability to cool the incoming supply air due to the integration of heat pipe system with the wind tower unit. No other closed-loop passive ventilation system is currently able to regulate air temperature, and no mechanical system is able to do so with as little energy input. FREECOOL can provide thermal comfort to occupants in hot climates by cooling incoming air without significant energy demand. This expands the operational window of wind towers in these regions when outdoor air temperature is too high to ordinarily be directly introduced into an occupied space. Typical wind tower systems must be closed when outdoor air temperatures rise above indoor air temperatures, as this no longer provides a cooling effect for occupants. The cooling effect of FREECOOL also provides an energy and greenhouse gas reduction as less energy is required for thermal comfort compared to mechanical HVAC systems. It is not envisaged that FREECOOL systems will be able to replace mechanical HVAC systems, instead the intention is to act as a complimentary technology to reduce demand on HVAC systems. It is estimated that in peak summer conditions in the UAE, where ambient air temperatures can reach 45°C, FREECOOL will reduce incoming air temperature by up to 15°C. Therefore, the mechanical HVAC units will be cooling air from 30°C, as opposed to 45°C. This will significantly reduce the demand on HVAC systems by up to 50%. Further information relating to this can be found in Appendix A. As the green and sustainable technologies sector grows, the economic growth of these technologies and sector will similarly develop. This new emergent field of passive cooling ventilation will provide a significant economic benefit. Job creation as a result of growth will benefit the local economy for contractors and installation, along with manufacturing and design employment opportunities. A further benefit of FREECOOL is the historical and cultural connection the design has with the people of the UAE and other Middle Eastern countries. Baud-geer are the traditional wind towers that were developed centuries ago for ventilation and cooling. The vernacular architectural designs have a strong heritage in the area but have fallen out of favour with modern society’s reliance on energy intensive mechanical HVAC systems. Modern wind towers are based on baud-geer, with modern technologies used to improve the performance. This link with traditional technologies compared to mechanical HVAC systems is hoped to bring about a change in attitude of those in the area; a move away from energy intensive mechanical systems, to passive designs with strong cultural links with traditional architecture of the area. The hope is that this leads to a greater uptake in the passive systems, providing more widespread energy reduction as the popularity of the system improves. This provides a societal impact, whereby the installation and increase in green technology ownership is seen as a positive movement.