US warms to thermal cooling projects

The US Department of Energy is funding a range of projects to develop innovative energy efficiency solutions for residential and commercial buildings – several of which focus on thermal cooling. Andrew Williams takes a look.

In recognition of the pressing need to improve energy efficiency performance in residential and commercial buildings, the DOE’s Building Technologies Office recently awarded a total of $83mn in funding to 44 projects under the auspices of its Buildings Energy Efficiency Frontiers & Innovation Technologies (BENEFIT) programme.

Several of the projects focus on the development of innovative thermal cooling and sustainable air conditioning technologies. One notable initiative is a project led by Delaware-based Baryon Inc. The firm is developing a novel air conditioning system based on a new method of evaporative cooling combined with dehumidification through an innovative ionic membrane.

As Demis Pandelidis, Founding Director at Baryon Inc, and inventor of the system, explains, the new technology utilises some of the principles of evaporative cooling, but: ‘works in a completely different airflow regime which, combined with membrane dehumidification, allows it to achieve high effectiveness in humid climates.’ Crucially, Pandelidis points out that the system also enables the same ‘comfort of use’ as traditional systems – including the same level of temperature control and thermal comfort, regardless of outdoor conditions.

‘The proposed unit achieves a coefficient of performance (COP) on the level of 12.5 in humid climatic conditions, which allows it to save 50–80% more energy in comparison to existing devices. It also has a simple plug-and-play structure that can be easily installed in any building and allows for independent temperature and humidity control,’ he says.

‘The additional benefit is that our unit produces water for its operation, meaning there is no external water consumption. This is a critical factor in many of the world’s regions and we are happy that we can meet this goal,’ he adds.

Functional prototype

The project aims to create the first energy saving solution for air conditioning systems in humid climates. Although many novel renewable energy-based devices have been implemented for heating purposes over the last two decades – including heat recovery units, heat pumps and solar PV systems – Pandelidis points out that no devices based on renewable energy have been widely applied in the cooling sector.

Although direct and indirect evaporative air-cooling technologies enable users to save energy in specific applications in dry climates, Pandelidis notes that their effectiveness drops significantly in moderate and humid climates – and they are not able to maintain comfortable conditions inside buildings in humid climates.

‘Most of the global human population lives in humid climates – with East and Southeast Asia, most states of USA, excluding central states like Nevada or Arizona, southern Europe and Africa all characterised by humid conditions in summer. For this reason, evaporative cooling can’t be widely applied and is only used in selected dry regions, like central parts of the US, as well as Australia and the Middle East,’ he says.

‘In addition, they consume high amounts of water, which is problematic in many regions with limited water supply – for example, in California. They also have fixed, large dimensions and lack temperature control capabilities because they are passive and their effectiveness depends on the ambient air conditions.’

In an effort to address these shortcomings, Pandelidis reveals that the goal of the Baryon project is to overcome all of the disadvantages of traditional evaporative cooling and take cooling technology to a completely new level. Building on earlier work to prove the principles of the technology at the laboratory and numerical level, the project will develop and install a fully functional prototype – verified by both the Argonne and Oak Ridge National Labs – that will serve as a base for mass production.

According to Pandelidis, a key benefit of the system is that it can be applied to any object that requires air conditioning in residential, commercial and industrial settings. Another major advantage of the proposed system is that it uses more than two times less energy.

‘The first target market for the system will be one-story commercial buildings – for example big-box, supercentre and warehouse club stores – due to the fact that the implementation process for such objects is relatively easy. Later we plan to approach all commercial and residential market sectors,’ adds Pandelidis.

Dual mode technology

Elsewhere, a project led by researchers at the University of Maryland will develop and validate an integrated 5–10 tonne heat pump and thermal energy storage system that can operate in both cooling and heating modes. The technology is said to achieve more than 50% demand reduction for four hours and more than 20% total energy efficiency improvement for all modes at a cost of less than or equal to $15/kWh.

As Daniel Bacellar, Assistant Research Professor in the Center for Environmental Energy Engineering (CEEE) at the University of Maryland, explains, the proposed technology consists of a dualpurpose (heating and cooling) thermal battery with room temperature storage integrated with a heat pump. The battery serves as a heat reservoir that absorbs heat when operating as a condenser in cooling mode, or rejects heat when operating as an evaporator in heating mode.

The system may also be configured as a single heat pump with one compressor, preferably two-stage, or two compressors, or two separate heat pumps with dedicated compressors.

‘Electricity consumption from commercial and residential buildings in the US dedicated to powering HVAC&R equipment is, respectively, more than 40% and 70% of the total consumption. Energy storage is a key for more efficient energy management; more specifically, for HVAC&R, thermal storage has potential for higher energy conversion, transfer efficiencies and possible lower costs than conventional electrochemical batteries,’ says Bacellar.

Distributed demand

For Bacellar, the key innovation of the technology is the fact it possesses a single reservoir through which heat is rejected or absorbed that is always at the same temperature. This means that system performance will be independent from outdoor conditions, unlike existing standalone heat pumps. When temperatures are too high or too low, the heat pump doesn’t need to work as hard when operating with the thermal battery, thus imposing less strain on the grid and resulting in more distributed demand throughout the day.

‘More commonly, thermal storage is used to store the cooling or heating load directly, requiring a separate storage for each mode; in this technology a single storage can deliver both,’ says Bacellar.

Looking ahead, Bacellar reveals that the project team – which also includes HVAC company Rheem, as well as Heat Transfer Technologies, Oak Ridge National Laboratory and the Electric Power Research Institute – will together develop a full commercialisation plan. ‘The project will focus on commercial buildings where we see an easier path to implementation. However, in principle, any air source heat pump could benefit from this technology,’ he adds.