Technology & Engineering
Heat Pump
A heat pump is a device that transfers heat from a lower temperature to a higher temperature using mechanical energy. It can be used for both heating and cooling purposes and is an energy-efficient alternative to traditional heating and cooling systems. Heat pumps are commonly used in residential and commercial buildings to provide comfortable indoor temperatures while reducing energy consumption.
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12 Key excerpts on "Heat Pump"
eBook - ePub- Anton A. Kiss, Carlos A. Infante Ferreira(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
CHAPTER 1 Introduction to Heat Pumps 1.1 INTRODUCTION A Heat Pump (HP) is a device that transfers energy from a heat source to a heat sink (destination) and upgrades the energy to a higher temperature level. Heat Pumps are designed to move heat in the opposite direction of normal heat flow by taking heat from a colder space and releasing it to a warmer one. Although the overall process seems to allow the heat to flow from the cold source to the warm destination, the normal heat flow from high to low temperature is respected in each step of the process. Note that a Heat Pump uses a certain amount of work (external power) to accomplish the transfer of energy from the heat source to the heat sink. The most common examples are refrigerators, air conditioners (ACs) and reversible-cycle Heat Pumps for providing thermal comfort. Notably, the term Heat Pump is more generic; it applies to many heating, ventilating and air conditioning (HVAC) devices used for space heating or cooling. When used for heating, a Heat Pump employs the same refrigeration-type cycle used by an air conditioner, but in the opposite direction – thus drawing heat from the ground or external air and releasing the heat into the air-conditioned space rather than the surrounding environment. Heat Pumps have several key advantages: very high efficiency as compared to gas-heated systems; the possibility to use environmental renewable energy from the air, water or ground; large energy savings of 50%–70% translated in reduced final and primary energy demand and significant reductions in greenhouse gas (GHG) emissions (e.g. CO 2). Nonetheless, Heat Pumps also have some drawbacks: An initial investment is needed (so payback times might be an issue), an electrical connection is required to be present typically and some refrigerants used in a Heat Pump are toxic or flammable (health, safety, environment [HSE] issues)
- Joshua Bird, Iona Norton, Ilaria Ricci Curbastro and Michael Edwards (Arup)(Authors)
- 2021(Publication Date)
14 Heat Pump instal lations for multi-unit residential buildings 4 Select technology, heat source and level of centralisation 4.1 Heat Pump technology Thermal energy can be moved from a colder to a warmer condition when there is an addition of energy (or work – second law of thermodynamics). Heat Pumps do this by using electrical energy to drive a vapour compression refrigeration cycle (Figure 8). Electrically driven Heat Pumps are a low-carbon technology rather than a zero-carbon technology. This is because the carbon emissions that result from their operation relate to the carbon intensity of the electricity grid and how this changes over time. The efficiency of a Heat Pump is the ratio between the useful work (heating or cooling) and the electrical input energy. When a Heat Pump is producing heat, the efficiency at any given point in time is described by the coefficient of performance (CoP), equal to the ratio between the heat transferred to the heat sink at the condenser and the electricity consumed. When a Heat Pump is providing cooling, the efficiency at any given point in time is described by the energy efficiency ratio (EER), equal to the ratio between the heat extracted from the heat source at the evaporator and the electricity consumed. Heat source Heat distribution, storage and use Gas refrigerant High pressure warm Evaporating Low pressure cool Expansion Compression Condensing Liquid refrigerant Heat Pump 66% free environmental energy + 33% electrical energy = 100% heating energy Figure 8 Working principle of a Heat Pump (courtesy of Chris Twinn) Heat Pumps and refrigerants Following phase out of chlorofluorocarbon gases (CFCs), and due to the ongoing phase-down of hydrochlorofluorocarbon gases (HCFCs) under the Montreal Protocol, the Heat Pump, refrigeration and air conditioning industry has moved towards hydrofluorocarbon (HFC) refrigerants such as R134a and R410A.
eBook - ePub- Simon Rees(Author)
- 2016(Publication Date)
- Woodhead Publishing(Publisher)
1An introduction to ground-source Heat Pump technology
S.J. Rees University of Leeds, Leeds, United KingdomAbstract
Ground-source Heat Pumps (GSHPs, or geothermal Heat Pumps) have great appeal in offering levels of efficiency for building heat and cooling that are – both theoretically and practically – higher than other technologies. This chapter introduces the technology and reviews its historical development and current state of exploitation around the world. Current challenges and prospects are discussed.Keywords
Carbon emissions; Development; Ground-source Heat Pump technology; History; Outlook; Policy1.1. Introduction to the technology
1.1.1. Heat Pump principles
Heat Pumps are a form of heat engine that uses mechanical work to transfer heat from a low temperature source to a higher temperature sink. There are a wide range of applications of Heat Pumps but in this context we are concerned with transferring heat between buildings and the external environment – either rejecting heat to the environment and cooling the building or extracting heat and heating the building. Although various forms of thermodynamic cycle can be used to move heat between source and sink, the predominant form is based on the vapour–compression cycle in which a refrigerant gas is evaporated, compressed and condensed in turn to transfer heat. The principle components in the cycle are shown in Fig. 1.1 . The state of the refrigerant throughout the cycle is well illustrated in an enthalpy–pressure diagram such as that on the right of this figure. The enthalpy changes in the condenser and evaporator indicate the heat transfer rate per unit mass of refrigerant flowing. Chapter ‘New trends and developments in ground-source Heat Pumps
eBook - PDFRefrigerators, Heat Pumps and Reverse Cycle Engines
Principles, State of the Art and Trends
- Jocelyn Bonjour(Author)
- 2023(Publication Date)
- Wiley-ISTE(Publisher)
Heating and Cooling by Reverse Cycle Engines: State of the Art 5 A Heat Pump is, from a thermodynamic point of view, no different from a refrigerator: in both cases, it is a thermal generator which, thanks to energy consumption, transports heat from a cold source to a hot source. Thus, the previous systems, qualified as “refrigerators”, can all be used as a Heat Pump. The difference between these two types of machines lies in how they are used. What is interesting about a Heat Pump is the quantity of heat which will be supplied to the hot source. This difference of interest gives the definition of the coefficient of performance (COP): = | | ௪ [1.7] This relation is, according to the first law (| | = + ), always greater than 1, meaning that these systems are of great theoretical and practical interest. Indeed, unlike other heating processes, this one makes it possible to obtain thermal energy greater than the energy expended to obtain it. The difference of course comes from the energy “pumped” into the cold source. With the theoretical and technological development of Heat Pumps being modeled on that of refrigerating systems, there is no need to repeat it here. Emphasis will simply be placed on the difference between the definitions of the energy efficiency ratio ε, on the one hand, and of the COP, on the other hand, which of course leads to differences in expressions. For example, the COP of a Heat Pump operating according to the Carnot cycle is: ௧ = [1.8] The relative coefficient of performance corresponds to the exergy efficiency ௫ (if the reference temperature is equal to the temperature of the cold source) of a Heat Pump and is given by: ௧௩ = ை ை ೝ [1.9] 1.1.2. Actual cycle with superheating and subcooling Figure 1.3 shows a diagram of a refrigerator (or Heat Pump), as well as the evolution cycle of the associated refrigerant.
- Albert Thumann, Scott C. Dunning(Authors)
- 2020(Publication Date)
- River Publishers(Publisher)
Chapter 7 , it was seen that the direction of heat flow is from hot to cold. Basically, energy or pumping power is needed to make heat flow “up hill.” The mechanical refrigeration compressor “pumps” absorbed heat to a higher level for heat rejection. The refrigerant gas is compressed to a higher temperature level so that the heat absorbed by it (during the evaporation or cooling process) is rejected in the condensing or heating process. Thus, the Heat Pump provides cooling in the summer and heating in the winter. The source of heat for the Heat Pump can be from one of three elements: air, water or the ground.Air-to-air Heat Pumps
Heat exists in air down to 460°F below zero. Using outside air as a heat source has its limitations, because the efficiency of a Heat Pump drops off as the outside air level drops below 55°F. This is because the heat is more dispersed at lower temperatures, or more difficult to capture. Thus, Heat Pumps are generally sized on cooling load capacities. Supplemental heat is added to compensate for declining capacity of the Heat Pump. This approach allows for a realistic first cost and an economical operating cost.Heat Pumps Do Save Energy
An average of 2 to 3 times as much heat can be moved for each kW input compared to that produced by use of straight resistance heating. Heat Pumps can have a COP of greater than 3 in industrial processes, depending on temperatures. Commercially available Heat Pumps range in size from two to three tons for residences to up to 40 tons for commercial and industrial users. Figure 8-1
eBook - ePub- Frank Kreith, D. Yogi Goswami, Frank Kreith, D. Yogi Goswami(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
9Heat Pumps
Herbert W. Stanford IIICONTENTS
9.1 Heat Pump Concept 9.2 Air-Source Heat Pumps 9.2.1 Premium Efficiency Air-Source Heat Pumps 9.2.2 Cold Climate Air-Source Heat Pumps 9.2.3 Dual Fuel Air-Source Heat Pumps 9.3 Water-Source Heat Pumps 9.3.1 Closed-Circuit Water-Source Heat Pump Systems 9.3.2 Closed-Circuit Geothermal Heat Pump Systems 9.3.3 Open-Circuit Geothermal Heat Pump Systems 9.3.4 Gas-Fired Engine-Driven Heat Pumps 9.3.5 Heat Recovery Chiller/Heat Pump System 9.3.6 Variable Refrigerant Flow Heat Pump System 9.4 Advanced-Technology Heat Pumps 9.4.1 Absorption Cycle Heat Pumps 9.4.2 Solar-Assisted Heat Pumps Bibliography9.1 Heat Pump Concept
Heat Pumps are reverse cycle building heating/cooling units or systems that can extract heat from a building and reject that heat to the environment, providing cooling for a building, and can switch from providing cooling to providing heating by extracting heat from the environment and rejecting that heat into a building . This heat transfer cycle can be accomplished using a vapor-compression refrigeration cycle or an absorption refrigeration cycle; though by far, vapor-compression systems are more widely used (see Section 9.4 for more discussion of absorption cycle systems).All refrigeration cycles hinge on one common physical characteristic: if a chemical compound (which we can call a refrigerant ) changes phase from a liquid to a gas, a process called evaporation , the compound must absorb heat to do so. Likewise, if refrigerant changes phase back from a gas to a liquid, the process of condensation , the absorbed heat must be rejected. Thus, all refrigeration cycles depend on circulating a refrigerant between a heat source (from which heat is removed, thus producing cooling) and heat sink
eBook - ePub- Jürgen Bonin(Author)
- 2015(Publication Date)
- Taylor & Francis(Publisher)
3 What is a Heat Pump and how does it work?A Heat Pump is a ‘refrigerating machine’, a machine usually used for cooling (e.g. a refrigerator). It works by removing heat from an interior space through cooling. This extracted heat must subsequently be released elsewhere. In a refrigerator, this is achieved using a cooler (condenser), which emits the heat into the ambient air.Heat Pumps or refrigerating machines have a long history. The first safe and functional ammonia-refrigerating machine was built by Carl von Linde in 1876. This marked the start of the combined use of cold and heat.Figure 3.1 1876 – Carl von Linde built the first refrigerating machineFigure 3.2 The refrigerator – a Heat Pump refrigerating machine3.1 Why is a Heat Pump called a ‘Heat Pump’? The term ‘Heat Pump’ can be explained using the following diagram. A Heat Pump ‘pumps’ heat from a lower temperature level to a higher temperature level.Figure 3.3 shows a water-water Heat Pump: it extracts heat from groundwater with a temperature of 10 °C by cooling it to 7 °C. This extracted heat is used, for example, for heating water to a flow temperature of 35 °C. After being used for underfloor heating, for example, the heating water subsequently flows back to the Heat Pump at 5 °C lower (i.e. it is returned at 30 °C).Figure 3.3 Temperature levels in a Heat PumpThus the Heat Pump has pumped heat from 10 °C to 35 °C. The Heat Pump has to work in order to reach this temperature level. This requires energy, usually in the form of electricity drawn from the mains supply.When it comes to generating hot water, the Heat Pump needs to ‘pump’ the ‘heat’ to a higher temperature level, to a flow temperature of 55 °C. The Heat Pump has to work harder to reach this higher flow temperature, and this requires more electrical energy.That means:• The higher the required flow temperature, the harder a Heat Pump needs to work. Therefore, it is extremely important that the temperature difference between the heat source (e.g. groundwater, brine or air) and thermal heat (e.g. flow temperature for heating) is as small as possible.
eBook - PDF- Frank Kreith, D. Yogi Goswami, Frank Kreith, D. Yogi Goswami(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
229 9 Heat Pumps Herbert W. Stanford III 9.1 Heat Pump Concept Heat Pumps are reverse cycle building heating/cooling units or systems that can extract heat from a building and reject that heat to the environment, providing cooling for a building, and can switch from providing cooling to providing heating by extracting heat from the environment and rejecting that heat into a building . This heat transfer cycle can be accom- plished using a vapor-compression refrigeration cycle or an absorption refrigeration cycle; though by far, vapor-compression systems are more widely used (see Section 9.4 for more discussion of absorption cycle systems). All refrigeration cycles hinge on one common physical characteristic: if a chemical compound (which we can call a refrigerant ) changes phase from a liquid to a gas, a pro- cess called evaporation, the compound must absorb heat to do so. Likewise, if refrigerant changes phase back from a gas to a liquid, the process of condensation, the absorbed heat must be rejected. Thus, all refrigeration cycles depend on circulating a refrigerant between a heat source (from which heat is removed, thus producing cooling) and heat sink (some- where to which the collected heat can be rejected). CONTENTS 9.1 Heat Pump Concept .......................................................................................................... 229 9.2 Air-Source Heat Pumps .................................................................................................... 232 9.2.1 Premium Efficiency Air-Source Heat Pumps .................................................... 232 9.2.2 Cold Climate Air-Source Heat Pumps................................................................ 234 9.2.3 Dual Fuel Air-Source Heat Pumps...................................................................... 234 9.3 Water-Source Heat Pumps................................................................................................
eBook - ePubA Handbook on Low-Energy Buildings and District-Energy Systems
Fundamentals, Techniques and Examples
- L.D. Danny Harvey(Author)
- 2012(Publication Date)
- Routledge(Publisher)
fiveHeat Pumps
Heat Pumps can be used for heating, air conditioning and the production of hot water. Residential air conditioners and commercial chillers operate on the same principles as Heat Pumps, so they can be thought of as Heat Pumps that operate in only one direction, to cool buildings. Indeed, in some parts of the world (such as Japan), the majority of air conditioners are reversible, so they are really Heat Pumps. In any case, much of the information presented in this chapter is applicable to air conditioners and commercial cooling equipment, and so forms a complement to Chapter 6 , where this equipment is discussed.5.1 Operating principles
The natural tendency of heat is to flow from warm to cold. A Heat Pump transfers heat against its natural tendency, from cold to warm, in the same way that a bicycle pump moves air against its natural tendency, from low pressure (outside the tyre) to high pressure (inside the tyre). In both cases, work must be done (requiring energy).There are two broad types of Heat Pumps, based on either a vapour compression cycle or an absorption cycle. A vapour compression Heat Pump can be powered by electricity or by mechanical shaft power. The latter is used in industry and sometimes in the central cooling plants of district cooling systems. An absorption Heat Pump uses heat rather than electricity or mechanical power as the energy input to drive the Heat Pump. Absorption chillers (used for cooling purposes only) are much more common than absorption Heat Pumps (used for cooling and heating). Electric vapour compression Heat Pumps are widely available and have been mass marketed for decades. Thus, this chapter focuses on electric vapour compression Heat Pumps, while absorption (and other) chillers are discussed in Chapter 6 .An outline of how an electric vapour compression Heat Pump works is found in Box 5.1. The transfer of heat from cold to warm is accomplished through a compression—expansion cycle involving a refrigerant or working fluid. If heat needs to be transferred from the outside to the inside of a building, the refrigerant must be cooled (through expansion) to a temperature colder than the outside, so that it can absorb heat from the outside. This absorption occurs through a heat exchanger —a coil through which the refrigerant flows as outside air is blown past it. As the refrigerant absorbs heat, it evaporates rather than increases in temperature, so the heat exchanger is called an evaporator. Once inside the building, the refrigerant must be warmed (by compressing it) to a temperature warmer than the medium to which the heat is transferred (either air or water), so that it will release heat to the inside. Once again, the heat transfer occurs through a heat exchanger, which maximizes the contact area between the warmed refrigerant and the air or water to be heated. As heat is released from the working fluid, the working fluid condenses rather than decreases in temperature, so this heat exchanger is called a condenser. The difference between the evaporator and condenser temperature is referred to as the temperature lift.
No longer available |Learn more- John Siegenthaler(Author)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 532 C H A P T E R 1 3 Air-to-Water Heat Pump Systems In a heating-only application, the Heat Pump’s evaporator always gathers low-temperature heat from some source where heat is freely available and abundant. The condenser always delivers higher temperature heat to a load. One example is a Heat Pump that is only used to heat a building. Another would be a Heat Pump that only delivers energy to heat domestic water. In a cooling-only application, the Heat Pump’s evaporator always absorbs heat from a media that is intended to be cooled. The condenser always dissipates the unwanted heat to some media that can absorb and dissipate it (i.e., outside air, ground water, or soil). Examples would include a common air conditioner that can only remove heat from a building. Another would be a water-to-water Heat Pump that is used to chill water as part of an ice-making process. Although there are several applications where non-reversible Heat Pumps can be used, one of the most unique benefits of modern Heat Pumps is that the refrigerant flow can be reversed to immediately convert the Heat Pump from a heating device to a cooling device. Such Heat Pumps are said to be reversible. A reversible Heat Pump that heats a building in cold weather can also cool that building by removing heat from it during warm weather. Reversible Heat Pumps contain an electrically operated device called a reversing valve . An example of such a valve is shown in Figure 13-7. The first law of thermodynamics dictates that, under steady state conditions, the total energy input rate to the Heat Pump must equal the total energy output rate.
eBook - ePubAn Introduction to Thermogeology
Ground Source Heating and Cooling
- David Banks(Author)
- 2012(Publication Date)
- Wiley(Publisher)
condenser. This allows us to answer the tantalising question – is it sensible to leave the door of the fridge open on a hot summer’s day to cool your kitchen? Although opening the fridge door might bring some temporary relief, as cool air flows out into the kitchen, the long-term answer is ‘no’. The fridge’s Heat Pump will simply be transferring energy from the kitchen in front of the fridge, via the open door, to the kitchen at the back of the fridge. And with each cycle of the Heat Pump, say, 100 W of electrical energy is being converted to heat energy and being added to the discharged heat load. This tempting practice will steadily lead to your kitchen heating up.4.5 Absorption Heat Pumps
Finally, it should be noted that we can even design Heat Pumps that do not use mechanical compressors, but which use heat as their energy source. You may be familiar with the gas-powered fridge, where bottled gas is burned to chill a food cabinet and which is very useful in parts of the world where mains electricity is unreliable or non-existent. This gas fridge is a form of Heat Pump called an absorption Heat Pump (Box 4.5). It functions in an analogous cycle to the ‘conventional’ version, but the compressor is replaced with a chemical absorption reaction and the electrical energy source is replaced with a heat source (e.g. a gas burner). Thus, we can use heat to transfer even more heat – to produce either space heating or chilling. This is especially important in the context of ‘trigeneration’ (Box 4.3) – if we have surplus heat from a hot geothermal well, a CHP plant or an industrial process, we can use it to provide chilling (air conditioning, district cooling) in summer. There are now marketed ground source absorption Heat Pumps, for space-heating purposes, running on the combustion of mains gas and offering competitive efficiencies (Robur, 2010).BOX 4.5 The Absorption Heat PumpThe absorption Heat Pump or refrigerator is not hugely different from a vapour compression–expansion unit. The absorption cycle uses a heat source, rather than mechanical or electrical energy, as its energy input. The compressor is replaced by an ‘absorber’ – a reservoir of absorbent medium, in which the cycling refrigerant has a high solubility. The ‘classic’ combination, utilised by Carré in 1858–1859, was water as the absorbent and ammonia as the refrigerant. The ammonia may be mixed with a low-solubility carrier gas, such as hydrogen, which does not take part in the refrigeration process, but which essentially regulates pressure in the system. Other combinations could be used: historically, water (refrigerant) and sulphuric acid (absorbent) were employed, or, in more recent times, water (refrigerant) and lithium bromide (absorbent).
- Ursula Eicker(Author)
- 2014(Publication Date)
- Wiley(Publisher)
Chapter 8
Compression chillers and Heat Pumps
Figure 8.1 Youth center L-Quadrat in Ostfildern with passive energy standard and ground source Heat Pump (Photo: Barta).Figure 8.2 Heat Pump with vertical ground heat exchangers in the youth center Ostfildern (Photo: Barta).As renewable electricity fractions have increased strongly in the last decade, heating or cooling using electrically driven Heat Pumps or compression chillers offer new possibilities for renewable energy supply.Power generated by photovoltaic (PV) modules has become so cheap that electrical compression cooling using PV power has become an interesting option for solar cooling. Primary energy efficiencies are comparable to solar thermal cooling and depending on energy prices, feed-in tariffs and investment costs, PV cooling systems can be at the same level or even cheaper than solar thermal systems. Heat Pumps can supply heating and domestic hot water most efficiently, if the supply temperature levels are low.8.1 Overview of Heat Pump and chiller technologies
Heat Pumps or chillers can be basically divided into two types; sorption Heat Pumps, in which the cold vapour is compressed by heating a solvent, which has absorbed the refrigerant vapour, and the compression Heat Pump, which is currently the predominant technology used in Heat Pumps and air conditioning.In compression Heat Pumps, the suction of the gaseous refrigerant from the evaporator and subsequent compression is carried out by an electrically- or combustion-driven mechanical compressor.The term ‘Heat Pump’ describes only the machine itself. A decisive factor for efficiency and costs of a Heat Pump system is the temperature level of the environmental heat source, from which heat can be extracted, with efficiency rising with temperature level of the heat source.
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