Gas driven heat pumps : market potential, support measures and barriers to development of the UK market

There are currently two domestic or near domestic gas heat pumps available in the EU. One is a nominal 38 kW ammonia-water machine manufactured by Robur in Italy and badged by a number of manufacturers. The other is a 10 kW water-zeolite adsorption unit made by Vaillant in Germany. Viessmann has a similar adsorption machine about to go on the market and is working on a second generation absorption machine that is physically much smaller. Other companies are working on gas-fired domestic heat pumps but are at an earlier stage of development. The largest potential market for gas heat pumps is the UK. Gas heat pumps have the potential to take a share of the boiler replacement market which is around 1.4 million p.a. and of which 30% are system boilers rather than combi boilers. The route by which boilers pass from manufacturer to private householder is dominated (79%) by contractor/installers who buy from builders merchants and this must be the target route if there is to be a widespread uptake of gas heat pump technology. Important factors for the contractor/installer are: Familiarity with boiler (installed them before, received training from manufacturer, accredited installer) Easy and quick to install (weight/ fittings). Must be a ‘one man fit’. Good back-up support from manufacturer should there be a problem e.g. spares available The consumer’s main concerns are capital cost and efficiency. The limit on payback time for the average consumer is about three years. The new build or major refurbishment market is smaller than the retrofit but still significant (175,000 p.a.). In this case the contractor/installer has much less influence and codes / regulations play a greater role. Specifier/Installer training is an important issue. MIS 3005 is being adapted for gas heat pumps and future products may not be so demanding in terms of installer competencies. Consumer behaviour is an issue, the UK consumer being wary of new technology. Capital cost is also important and inclusion of gas heat pumps within the RHI could tackle both issues. Safety and noise, whilst of obvious importance are not seen as the main challenges. Inclusion in the RHI with a suitable tariff is the most appropriate and effective means of support available. EN standards (safety and performance) for gas heat pumps exist and are presently being improved. The MCS is defining a minimum acceptable level of performance, together with the methodology for calculation. Eco Design for Energy Using Products (EuP) standards are still in the process of being drawn up. Work on scenarios to 2050 suggest that gas may still have a place in the longer term and that (used in gas heat pumps) it might find most use in older and larger dwellings

State of the art in gas driven heat pumps

All of the products currently on the market or known to be under development are being developed by European companies. The market leader is Robur, with ammonia-water absorption heat pumps available in air, water and ground source versions with nominal heat output around 40kW. GUEs in the different versions are higher than competitors. Water at up to 70 degrees Celsius can be produced but the GUE under these conditions is generally not available. A half-size version is under development. The present machines are single outdoor packages. Vaillant and Viessmann have water-zeolite adsorption machines on and near-market respectively. They are single indoor units, large in size, and when in heat pumping mode cannot produce water hotter than 55 degrees C. They use solar heated water (Vaillant) or ground source heat, air source being unfeasible with water as a refrigerant. Viessmann are developing a much more compact absorption machine, thought to use methanol as a refrigerant and capable of operating with air as a heat source. Other adsorption developments are in progress but further away from market. Improvements are needed in size and capital cost to achieve sales, but the efficiencies achieved by Robur are probably sufficient at least in the short term

Proof of concept car adsorption air conditioning system using a compact sorption reactor

A prototype compact sorption generator using an activated-carbon ammonia pair based on a plate heat exchanger concept has been designed and built at Warwick University. The novel generator has low thermal mass and good heat transfer. The heat exchanger uses Nickel brazed shims and spacers to create adsorbent layers only 4 mm thick between pairs of liquid flow channels of very low thermal mass. The prototype sorption generator manufactured has been evaluated under the EU car air conditioning testing conditions. While driven with waste heat from the engine coolant water (at 90°C), a pair of the current prototype generators (loaded with about 1 kg of a carbon in each of two beds) has produced an average cooling power of 1.6 kW with 2 kW peaks

Modelling the ammoniation of barium chloride for chemical heat transformations

The coupling of reversible ammoniation reactions between two salts presents a method for the exploitation of low grade waste heat. This resorption configuration can be used for thermal transformation or heat pumping, to recover waste heat to primary producers, or for integration in heat networks. To understand the solid/gas reaction behaviour and to model its kinetics, Large Temperature Jump (LTJ) experiments were performed on a composite of barium chloride in an expanded natural graphite (ENG) matrix. A model has been built using a semi-empirical equation from the literature, which has been validated with the LTJ results. The results suggest the semi-empirical model provides a reasonable prediction for solid/gas reactions once the constants have been identified. Enhancing the model to handle sequential phase change reactions will enable a wide number of salts to be modelled, making the design of a resorption system practicable

Carbon-ammonia pairs for adsorption refrigeration applications : ice making, air conditioning and heat pumping

A thermodynamic cycle model is used to select an optimum adsorbent-refrigerant pair in respect of a chosen figure of merit that could be the cooling production (MJ m(-3)), the heating production (MJ m(-3)) or the coefficient of performance (COP). This model is based mainly on the adsorption equilibrium equations of the adsorbent-refrigerant pair and heat flows. The simulation results of 26 various activated carbon-ammonia pairs for three cycles (single bed, two-bed and infinite number of beds) are presented at typical conditions for ice making, air conditioning and heat pumping applications. The driving temperature varies from 80 degrees C to 200 degrees C. The carbon absorbents investigated are mainly coconut shell and coal based types in multiple forms: monolithic, granular, compacted granular, fibre, compacted fibre, cloth, compacted cloth and powder. Considering a two-bed cycle, the best thermal performances based on power density are obtained with the monolithic carbon KOH-AC, with a driving temperature of 100 degrees C; the cooling production is about 66 MJ m(-3) (COP = 0.45) and 151 MJ m(-3) (COP = 0.61) for ice making and air conditioning respectively; the heating production is about 236 MJ m(-3) (COP = 1.50)

Development of a domestic adsorption gas-fired heat pump

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kühn – Berlin: Universitätsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]A gas-fired heat pump system intended to replace conventional condensing boilers is under development. The machine uses four sorption generators with heat recovery between all beds plus mass recovery and has a nominal heat output of 7 kW. Predicted annual average heating COP (Heat output / gas energy input based on gross calorific value) is 1.35 in a UK application with low temperature radiators. The system is described together with the simulation model, the test facilities and procedures

The Structural Determinants and Functional Consequences of Left Ventricular Outflow Tract Obstruction in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the commonest inherited cardiac condition. Many patients have resting or provocable left ventricular outflow tract (LVOT) obstruction. Symptoms treated with drugs or surgery may improve. There is a need to improve the clinical assessment in individual patients, because of the often poor correlation between symptoms and LVOT gradient, and the association with complications such as stroke, heart failure and sudden cardiac death. In addition, in a proportion of patients with significant LVOT gradients, relief of obstruction does not adequately improve symptoms. Reduced angulation between the inter-ventricular septum and the aorta is a determinant of LVOT obstruction. However, lack of a standardised method of measurement in HCM without recourse to complex 3-D imaging limits the usefulness of this parameter in routine practice. Transthoracic echocardiography is widely available, and can be used to measure aorto-septal angulation. However, data in HCM are lacking. I validated a simple measurement of aorto-septal angulation using 2-D echocardiography and cardiac magnetic resonance imaging and determined its relation to provocable LVOT obstruction in HCM. I showed this technique to be easy, reproducible, comparable to magnetic resonance imaging, and can be quickly calculated using standard echocardiographic software. Patients have a smaller aorto-septal angle than controls, where it is associated with higher peak LVOT gradient. A reduced aorto-septal angle is highly specific for provocable LVOT obstruction and should prompt further evaluation in symptomatic patients without resting gradients. I used a non-invasive technique for measuring cardiac output to determine the relation between LVOT obstruction, cardiac output and peripheral oxygen utilisation in patients with HCM during exercise. I demonstrated that cardiac output response to exercise is impaired, caused largely by failure to appropriately augment stroke volume. LVOT obstruction is associated with greater impairment of stroke volume at peak exercise and is an independent and modifiable predictor of cardiac output reserve. However, heterogenous responses are seen between patients who otherwise appear similar using standard clinical criteria. There is therefore a strong argument for the individualisation of therapy in patients with LVOT obstruction. Invasive therapies to reduce gradients may work better in those with genuine obstruction to the outflow of blood, rather than for example myocardial ischaemia or mitral regurgitation. The non-invasive measurement of haemodynamic indices during exercise is practical, aids understanding of the complex physiological basis behind symptoms and may help to tailor therapy for HCM, and in particular LVOT obstruction

Alternative monolithic/composite carbons for adsorption generators and simulation for optimal performance

This paper presents the development and thermal properties study of three types of carbon composites with enhanced thermal properties along with the optimisation of the geometry of the shell and tube generators currently used at the University of Warwick for the development of carbon-ammonia heat pumps. The three carbon composites developed use lignin binder, silanes binder and Expanded Natural Graphite (ENG) as a way of enhancing their thermal properties in order to perform more efficiently in a refrigeration or heating system. Two techniques were used in order to obtain the thermal properties: Anter and HyperFlash thermal conductivity instruments. Results show that ENG increases drastically the thermal conductivity of the samples (up to 3.4 W/(mK)) but reduces the carbon density (450 kg/m3) and increases the thermal mass of the system. Lignin binder samples show lower thermal conductivities (0.3 W/(mK)) but higher carbon densities (750 kg/m3) which increases the performance of the machine. Thermal conductivities of samples were also obtained for a wide range of working temperatures (25–200 °C). The current development of gas fired heat pumps at Warwick uses shell and tube adsorption generators with over 1000 water tubes of 1.2 mm diameter on a 3 mm pitch. This geometry is not optimised and a dynamic simulation program has been written to determine how far from optimal the design is and also whether alternative designs offer advantages. The results presented show that the shell and tube is close to optimal for its type but that finned tube designs might offer improvements

Study of thermal conductivity and geometry wall contact resistance effect of granular active carbon for refrigeration and heat pumping systems

The commercial success of sorption refrigeration and heat pump systems depends on a good heat and mass transfer in the adsorbent bed, which allows higher coefficients of performance and greater specific heating or cooling power that reduce capital costs. In this study the thermal conductivity and thermal contact resistance of vibrated and compressed granular active carbon and binary mixtures of active carbon are investigated using two types of conductivity measurements: a steady-state measurement between flat plates and a transient hot tube measurement. With these results is possible to draw conclusions on how the wall geometry, particle size distribution, and bulk density affect the overall thermal performance. Results show that using binary mixtures of grains and powder gives results superior to those of either grains or powder alone. The conductivity of the binary mixtures increases roughly linearly with bulk density and the 2/3 grain mixture achieves the highest densities. The method used to achieve compaction (vibration or compression) did not seem to affect the result. Thermal contact resistances reduce with increasing density but do vary with the mixture ratio, also appearing to be best with a 2/3 grain–1/3 powder mixture