Morten Boje Blarke

Large-scale heat pumps in sustainable energy systems: system and project perspectives

In this paper, it is shown that in support of its ability to improve the overall economic costeffectiveness and flexibility of the Danish energy system, the financially feasible integration of large-scale heat pumps with existing CHP units, is critically sensitive to the operational mode of the heat pump vis-à-vis the operational coefficient of performance (COP), which is set by the temperature level of the heat source. When using only ambient air as the heat source, the total heat production costs increases by about 10%, while the partial use of condensed flue gas from the CHP unit as a heat source results in an 8% cost reduction. Furthermore, the operational analysis shows that when a large-scale heat pump is integrated with an existing CHP unit, the projected spot market situation in Nord Pool towards 2025, which reflects a growing share of wind power and heat-bound power generation electricity, will reduce the operational hours of the CHP unit significantly, while increasing the operational hours of the heat pump unit. In result, a heat pump unit at half heat production capacity in combination with heat-only boiler represents as an alternative to CHP unit operation, rather than a supplement to CHP unit operation. While such revised operational strategy whould have an impact on electricity markets, the result indicates that in a sustainable energy system, either a large-scale heat pump should fully replace an existing CHP producer, or the size of the heat pump to be integrated with an existing CHP unit should be much below half of the CHP unit’s heat production capacity. The CHP with heap pump design should allow for both combined (CHP unit and heat pump) and sole operation (heat pump only).

Dynamic analysis of a dual-mode CO2 heat pump with both hot and cold thermal storage

We investigated the dynamics of a transcritical CO2 heat pump system including hot and cold thermal storages, which makes up the concept “thermal battery”. The analytical model is used for the study of the dynamics of the system involving simultaneous supply of heating and cooling for buildings. The model includes the dynamics of the gas cooler, evaporator and the thermal storages, while the compressor and the expansion valve are considered quasi-static. The heat transfer in the dynamically modeled components is described by partial differential equations (PDEs) consisting of heat conduction, convection, and source terms. Each component is divided into a number of volumes adjusted according to the required precision and reasonable computational time. We applied two discretization schemes in order to find a numerical solution to the PDEs. The spatial discretization for the heat exchangers is performed by using the upwind scheme, where the fluid properties are individually calculated within each volume. Due to the discrete events in form of tapping and loading (or charging and discharging) of the heat storages, the discretization approach takes into account the sharp spatial transitions within the thermal storages. Therefore, the method of lines in combination with the Superbee slope-limiter was applied for the spatial discretization for high resolution calculation. The modeling approach results in a set of algebraic and ordinary differential equations (ODEs), hence the model becomes an algebraic differential equation problem, which we solved by using MATLAB solver ODE15s.This extended model was used to simulate a dynamic response of the case with varying heating and cooling consumption over a period of 24 hours in a building. The heating and cooling energy consumption follow a sinusoidal and continuous pattern. The results include the effect on both the outlet temperatures and the system coefficient-of-performance (COP). The outlet energy from the hot storage and the cold storage is used for heating tap water and a chilled water space cooling application subject to temperature requirements. Dimensioning of both storages is crucial for obtaining the required temperatures. The model identifies the critical storage levels required to satisfy the periodic but out-of-phase combination of heating and cooling demands. The volume of the cold storage will have to be considerably larger than the hot storage due to the lower temperature difference.Copyright

A flexible and low cost experimental stand for air source heat pump for Smart Buildings

Energy systems are faced with the challenges of reducing dependency on fossil fuels, while handling increasing penetration levels of intermittent renewables such as wind and solar power. At the same time, the efficient consumption of energy is vital for avoiding the impacts from increasing fuel prices. A significant part of this challenge may be dealt with in the way space heating, space cooling, and domestic hot water production which is provided to residential and commercial buildings. Air source heat pumps (ASHP) are widely used conversion technologies for providing building thermal energy services; cooling, heating, and water heating. ASHP does not have a constant temperature for the primary source like: soil, ground water, or surface water heat pumps. In result, laboratory experiments and tests are faced by the problem of having to handle a wide range of conditions under which the evaporator is operated. In order to cover various climate conditions, performance and behavior must be tested for temperatures ranging from -30°C to 40°C and for various humidity levels. This paper presents a state-of-art experimental stand, named controlled lab environment (CLE or climatic box), for testing ASHP under controlled evaporator ambient conditions. A main purpose of the CLE is to test and verify the performance and behavior of a theoretical model of the ASHP as a basis for optimization and efficiency improvements. Together with thermal storage technologies and intelligent control system this technology may come to play a key role in the development of Smart Buildings in future energy systems. While experimental results are not yet available the paper presents the design considerations and schematics of the CLE. Furthermore, a thermodynamic model of an ASHP is presented.

Modeling and Experiments on Fast Response Thermoelectric Co-Generation for Intermittent Renewable Energy Sources

We present preliminary proof-of-concept experimental results on a thermoelectric heat pump system. In our previous work we proposed a thermal battery which would benefit from state-of-the-art heat pumps in order to provide useful cooling and heating. The preliminary analysis demonstrated the benefit of using excess electricity from intermittent renewable power sources, e.g. solar or wind, and converting it into the hot and cold water storage tanks typically used for residential applications. The time response of mechanical heat pumps is slow and their efficiency suffers from fluctuating electricity supplies. To overcome this issue, we propose thermoelectric (TE) co-generation systems that benefit from their fast response and scalability. Modeling has been performed to optimize the TE module for the effective harvesting of both heat and electricity from intermittent solar energy with response times in minutes. Throughout the modeling and experiments, the combined coefficient-of-performance (COP) is found to be 1.6, while the hot water is 52.5°C and cold water is 16.5°C, both from 22.3°C. The COP is moderate, but due to its quick response, the accumulated energy harvested by this thermoelectric system could be comparable to mechanical compressor systems.© 2012 ASME