Valerius Venzik

• Doctor of Engineering
• R&D Director at Carrier

In heat pumps, the use of refrigerants with a low global warming potential (GWP) gains importance due to increasingly strict regulations regarding their ecological impact. In this regard, hydrocarbons (HCs), hydrofluoroolefins (HFOs), and their mixtures are the most promising options due to their thermodynamic properties. Besides the impact of the...

In heat pumps, the use of refrigerants with a low global warming potential (GWP) gains improtance due the increasingly strict regulations regarding their ecologic impact. In this regard, hydrocarbons (HCs), hydrofluoroolefins (HFOs), and their mixtures are the most promising options due to their thermodynamic properties. Besides the impact of the r...

Air Source Heat Pumps (ASHPs) are a key technology in sustainable heating and cooling applications. Using air as heat source in cold climate conditions causes frost related performance degradation, and thus frequent defrosting is necessary. Typically, demand-based defrost initiation methods detect frost with sensors and initiate defrosting when a c...

Frost on the evaporator of a cold storage refrigeration system reduces cooling capacity and COP (Coefficient of Performance). Hence an energy-efficient defrosting process is crucial for economical operation. Various defrosting methods have been proposed in literature and their defrosting efficiency has been assessed. However, differing experimental...

High temperature heat pumps have a high potential to reduce carbon emissions in industrial processes by replacing conventional heating systems for low-pressure steam generation. However, heat pump performance is sensitive to the selected refrigerant, flow sheet, and operating conditions complicating the design process. Thus, we conduct a refrigeran...

The refrigerant used in heat pumps significantly influences the overall system performance. However, selecting a proper refrigerant is no trivial matter due to the heat pumps’ sensitivity to the selected flowsheet, components, and operating conditions. Herein, a holistic approach is used that covers all these interdependencies simultaneously consid...

This work presents an approach to the contextual integration of fluid selection and compressor design for the cycle design of efficient industrial heat pumps. The vapor-compression cycle of an air-water heat pump operated at 42 °C source and 82 °C target temperature is investigated as a theoretical case study. An optimization study is performed, wh...

Selecting a suitable fluid for heat pump applications is essential due to the strong influence of the fluid on the overall cycle performance. According to the current state of research, typically, fluid selection bases on the simple refrigeration cycle assessment. However, the flow sheet strongly influences the performance of each fluid and vice ve...

This work presents an approach to the contextual integration of fluid selection and compressor design for the cycle design of efficient industrial heat pumps. The vapor-compression cycle of an air-water heat pump operated at \SI{42}{\celsius} source and \SI{82}{\celsius} target temperature is investigated as a theoretical case study. An optimizatio...

Due to current regulations, alternative working fluids for heat pump systems have to be identified. Thereby, hydrocarbons (HC) and hydrofluoroolefins (HFO) are possible solutions. However, both fluid categories are at least mildly flammable and thus, result in additional safety regulations. In particular, regulations includes refrigerant charge lim...

During operation of air-source heat pumps under certain operating conditions frost forms on the evaporator fins. The frost decreases system efficiency and must therefore be removed at frequent intervals to achieve energy-efficient and thus economical operation. Compared to a conventional time-controlled defrosting strategy, in which a defrosting pr...

Within the present investigation, we evalute the interactions between the refrigerant, and the cycle configuration. The investigation includes three cycle configurations - the simple cycle, an internal heat exchanger cycle and a vapor injection cycle. We evaluate the seasonal coefficient of performance based on EN 14825 for binary mixtures based o...

Due to political regulations, environmentally friendly refrigerants must replace conventional alternatives (i.e., R134a) in heat pumps. Especially in residential applications, many theoretical studies in the literature prove that hydrocarbons meet many requirements and have suitable thermodynamic properties to increase the efficiency of refrigerati...

The working fluid in heat pumps is subject to a variety of requirements that must be met for efficient and safe operation. Furthermore, the number of market-available working fluids is continuously increasing due to the development of new mixtures. Therefore, this paper screens the market for alternative working fluids. Additionally, the performanc...

In practice, there are methods such as EN 15450 designing a heat pump system consisting of a heat pump, auxiliary heater, and thermal energy storage. In heat pumps, the refrigerant has a significant impact on the overall efficiency and thus on its sustainability. However, refrigerant selection is not considered in standard design procedures. Moreov...

Die Entstehung von Reif an den Lamellen des Verdampfers von Luft-Wasser-Wärmepumpen ist unvermeidlich, wenn die Lufttemperatur unter die Temperatur des Frostpunktes abgesenkt wird. Die Reifbildung senkt die Ener-gieeffizienz der Anlage, sodass das periodische Abtauen der Reifschicht notwendig ist. Stand der Technik ist eine zeitgesteuerte Abtauung,...

de Wärmepumpen lösen im Gebäudesektor vermehrt konventionelle Heizsysteme ab. Da Wärmepumpen im Betrieb neben elektrischer Energie ein Kältemittel verwenden, das ein Treibhauspotenzial besitzt, ist die Abschätzung ihrer Emissionen über den Lebenszyklus komplexer als bei konventionellen Technologien. In diesem Beitrag werden ökologische Bewertungsme...

Heat pump systems are the key technology towards the transformation to a sustainable building supply. While heating buildings with conventional technologies such as gas boilers is relatively easy to accomplish through high flow temperatures, heat pump systems are much more sensitive to changes in temperature demands and heat loads. Simultaneously,...

Während des Betriebs einer Luft-Wasser-Wärmepumpe bildet sich unter bestimmten Betriebsbedingungen Reif an den Lamellen des Verdampfers. Der Reif stellt eine zusätzliche thermische Isolierschicht dar, sodass die übertragene Wärmemenge am Verdampfer und damit auch die Anlageneffizienz sinkt. Der Reif muss deshalb in regelmäßigen Abständen abgetaut w...

Die Defossilisierung der Gebäudeenergieversorgung durch die Integration erneuerbarer Energiequellen erfordert eine ganzheitliche Betrachtung der Versorgungssysteme, um deren Einbindung zuverlässig bewerten zu können. Zur zuverlässigen Bewertung und maximalen Ausschöpfung des ökologischen und ökonomischen Einsparpotentials der vornehmlich volatilen...

Mainly to provide heat, the building sector accounts for about 18 % of overall global CO2 emissions. By exchanging conventional technologies in the near future, heat pumps are a key technology to systematically decarbonise the heat supply chain. The efficiency of a heat pump strongly depends on its compressor’s efficiency. Thus, the compressor is t...

Heat pumps are a high efficiency solution to provide both heating and cooling. Within heat pumps, however, a working fluid is used which is subject to increasingly strict regulations. Thereby, low global warming potentials as well as a zero ozone depletion potential need to be satisfied. Therefore, conventional working fluids will be replaced by al...

In this presentation, we investigated the influence of alternative vapor-compression flow sheets on low-GWP HFO refrigerants. The presentation was included within the Annex 54 workshop.

In Teil 1 dieses Beitrags (HLH Bd. 72 (2021) Nr. 3) wurde bereits erläutert, dass Wärmepumpen zukünftig eine wesentliche Rolle zur nachhaltigen Energieversorgung in allen Sektoren spielen werden. Maßgeblich dafür sind hohe Effizienzen der Energiewandlung. Die Wärmepumpeneffizienz hängt dabei insbesondere von den äußeren Randbedingungen der Wärmeque...

Heat pump systems are a key technology to replace conventional heating technologies such as gas-fired boilers towards a sustainable building sector. Especially in existing buildings, heat pump systems commonly consist of an air-source heat pump, an auxiliary heater and thermal energy storages. Compared to an almost constant energy efficiency of boi...

Zeotropic mixtures are widely discussed as alternative refrigerants for vapor‐compression cooling appliances and heat pumps. Mixtures can increase efficiency due to their nonisothermal phase change. In theoretical studies, zeotropic mixtures show significant benefits for efficiency if the temperature glide of the mixture matches the temperature cha...

This paper presents an approach to investigate the refrigerant’s influence on a reciprocating compressor. High-light of this model is the one-dimensional semi-physical approach, which is general fluid independent. Compared to compressor models from literature, this model handles with real gas behaviour. The applied fluid property models have been s...

The compressor’s performance is crucial for an efficient heat pump operation. In order to compare different refrigerants thermodynamically, efficiencies are often assumed constant and the influence of the construction form is neglected. The resulting steady-state comparisons allow first system insights without conducting expensive experiments. In d...

Der Gebäudesektor in Deutschland umfasst aktuell rund 19 Millionen Gebäude. In neun von zehn Fällen basiert die Wärmeversorgung dieser Gebäude auf der Verbrennung von Öl und Gas in konventionellen Heizungsanlagen (Gas- oder Ölkessel). Dies hat unter anderem zur Folge, dass etwa 30 Prozent des gesamten CO2 Ausstoßes in Deutschland auf den Gebäudesek...

In Teil 1 dieses Beitrags (HLH Bd. 72 (2021) Nr. 3) wurde bereits erläutert, dass Wärmepumpen zukünftig eine wesentliche Rolle zur nachhaltigen Energieversorgung in allen Sektoren spielen werden. Maßgeblich dafür sind hohe Effizienzen der Energiewandlung. Die Wärmepumpeneffizienz hängt dabei insbesondere von den äußeren Randbedingungen der Wärmeque...

Within a conference workshop, we present the Urban Energy Lab 4.0 - Refrigerant Lab and investigations, which we conducted in this Lab. We conclude our talks and lead to panel discussion to deduce the outlook for natural refrigerants in heat pumps: --- 1. “Introduction to Urban Energy Lab 4.0” by Prof. Dr. Rita Streblow --- 2. “Refrigerant Lab –An...

Zusammenfassung Aufgrund politischer Vorschriften, müssen die momentan gängigen Kältemittel (z. B. R134a) zukünftig durch umweltfreundlichere Fluide ersetzt werden. Eine wichtige Rolle spielen hierbei die natürlichen Kältemittel. Isobutan (R600a) und Propan (R290) sind Vertreter dieser Gruppe. Beide Fluide sind umweltfreundlich, kostengünstig, in g...

The global warming potential of many working fluids used nowadays for vapor compression refrigeration systems and heat pumps is very high. Many of such fluids, which are used in currently operating refrigerators and heat pumps, will have to be replaced. In order to avoid a redesign of the system, it would be very helpful if efficient and ecological...

The rising share of renewable energy sources in power generation leads to the need of energy storage capacities. In this context, also some interest in thermal energy storages, especially in a concept called pumped heat electricity storage (PHES), arises. One possible design of such a PHES system consists of a compression heat pump (HP), a thermal...

Fluids with high global warming potential, which are used in existing refrigeration cycles and heat pumps, will have to be replaced soon by less harmful fluids, but the fluid selection is difficult especially due to the unknown compressor performance. In this work a differential compressor model for reciprocating compressors is introduced which pre...

Zeotropic mixtures in heat pumps, based on thermodynamic analysis, should lead to higher coefficients of performance (COP) due to the temperature glide which decreases exergy losses in the heat exchangers. However, fluid mixtures influence every component of a plant and the total system performance. In addition to the various theoretical studies in...