Heat Pumps for the Home

2nd Edition

John Cantor, Gavin D J Harper

• Publisher: The Crowood Press
• Year: 2020
• Print ISBN: 9781785007798
• eBook ISBN: 9781785007804
• Topic: Technology & Engineering
• Subtopic: Construction & Architectural Engineering
• Index: Technology & Engineering

In recent years, heat pumps have emerged as a promising new form of technology with a relatively low environmental impact. Moreover, they have presented householders with an opportunity to reduce their heating bills. Heat pumps can heat a building by 'pumping' heat from either the ground or the air outside: an intriguing process which utilizes principles that are somewhat analogous to those employed in the domestic refrigerator. Armed with the practical information contained in these pages, homeowners will have the necessary knowledge to take advantage of this potentially low-carbon technology to heat their properties. Now in an updated new edition, Heat Pumps for the Home describes what a heat pump is, how it works, the different methods of pumping heat and the importance of an appropriate and well-planned installation. It also provides you with the information that you need in order to make up your own mind about whether a heat pump might be appropriate to your own circumstances, and also demonstrates what you need to do to in order to make the system work efficiently.

CHAPTER 1

HEAT PUMPS IN CONTEXT

What is a Heat Pump?

A heat pump is a device that can transfer (pump) heat in the opposite direction to its normal direction of flow. Rather than ‘producing’ heat (like any other heating method) it moves it. In fact, your fridge is a heat pump and it ‘pumps’ heat out of your food and then ejects the heat to the room via the warm grille at the back. But in the context of this book, the technology described is used to replace a conventional home heating system.

The heat delivered is not free because you do need some energy input to operate the system, but intriguingly heat pumps can produce far more useful heat energy than the energy input needed to drive them. Indeed, this is usually the motivation for installing one. Moreover, as electricity generation becomes ‘cleaner’ the net CO emissions in a correctly configured installation are normally much lower than those of conventional fuels, like oil or gas, that they might displace. For this reason, they are classed as a ‘low carbon’ technology and a recognized form of heating worldwide.

Why Heat Pumps?

Heating is expensive, both in money and environmental terms. Heat pumps can potentially reduce the amount of energy input required, so can reduce both cash and environmental costs. That’s it, in a nutshell.

Until relatively recently these ‘costs’ have not been considered a matter for concern: fuel has been cheap and the phrase ‘environmental impact’ didn’t even exist. With the twin problems of climate change and peak oil now looming, any approach that can reduce consumption of fossil fuels deserves attention, and heat pumps are definitely one of them.

Our options are either to generate energy from the natural forces of the waves, wind or rivers, collecting energy from the sun, or by reducing our needs through insulation and minimizing waste. Clearly a mix of strategies is needed. Heat pumps are sometimes categorized alongside renewables like wind, wave, solar and hydro, but heat pumps are only partly renewable since, at the present time, the energy input that is required is rarely from a renewable source. On the other hand, unlike most other renewables, they can operate on-demand at any time.

Heat pumps are also classified as a low-carbon technology and as such attract funding in the UK from the Renewable Heat Incentive (RHI).

The RHI income may cover the installation cost of your heat pump, and the rate usually relates to a ‘deemed’ quantity of heat that your house should need, assuming some basic energy saving measures have been adopted first. In some cases, heat meters are used to calculate the payment due. There is a domestic scheme, giving payments over seven years, whilst the commercial scheme pays over a twenty-year period. The payments are generally greater than the cost of the electricity to run the system.

The reason for such a generous offer is, in part, a means to assist the country to meet its carbon-abatement targets.

Looking to the future, the scenarios presented in the Centre for Alternative Technology’s zero carbon Britain and David MacKay’s sustainable energy – without the hot air, suggest that heat pumps will play a large and vital part at a time when electricity becomes the predominant form of energy. This is already becoming true as the production of mains electricity becomes progressively ‘cleaner’.

HISTORY OF HEAT PUMPS

Before the development of refrigeration there were no known ways of making things cold, other than the slight cooling effect due to the evaporation of water. The only ice that was available was stored from the winter or shipped from cold regions, as it was in very large quantities from northern America in the early 1800s.

About half a century later, scientists had generally agreed on the true nature of heat and that ‘cold’ was merely a lack of heat. They also developed ways of making fluids evaporate so as to cause very large reductions in temperature. Refrigeration and air-conditioning were born and have been under development ever since. The applications for heating were installed somewhat sporadically in the early days since, whilst heat pumps were known as a possible method of heating, they were rarely cost-effective, so there was little incentive to build them.

Some examples of early development:

■John Sumner carried out some pioneering work with ground-source systems in Norfolk in the 1940s.

■A revolutionary project, installed in the early 1950s at the London Festival Hall, took water from the River Thames and then returned it back slightly colder, thus extracting energy from this vast body of water. The system was driven by gas engines, but was sadly short lived.

■At around this time there were several examples of heating applications using the technology normally used for refrigeration.

■In the 1980s, when oil was becoming expensive, air-source heat-pumps were being manufactured in the UK by Eastwood Heat Pumps in Nottinghamshire. The enterprise was not long-lived; this was due in part to the relatively low cost of newly exploited North Sea gas, but also because these units were not wholly compatible with most UK buildings, which were poorly insulated and draughty.

■Meanwhile, in Norway and Sweden, the industry flourished due to differing circumstances. The abundance of hydro-electricity made the heat pump a viable proposition and they have already, owing to necessity, embraced the need to insulate their houses.

■America and many other countries have, in their own ways, pioneered this technology and adapted it for use in their specific circumstances. For example, many American systems use ducted air distribution, since this is more suitable for cooling, as required by many particular regions.

The Future of Heat Pumps

Over the years, heat pumps have undergone small developmental improvements, as have many technologies, from the bike to the boiler. The laws of physics cast limits on what is attainable, as evidenced by the internal combustion engine that has only improved modestly over the last 100 years (unlike electronics that improve in quantum leaps). It is unlikely that we will see any dramatic breakthrough with heat-pump design, just modest step-by-step improvements.

Where things will improve, however, is when manufacturers produce heat pumps in ever-greater numbers and manufacturing techniques evolve, so that things become more cost-effective. The area that currently requires the most attention, however, is that of the end-use of the equipment. From planning to installing, this is where we still have a lot to learn, as we hopefully realize what works well and what doesn’t.

Another important prerequisite for sustainable heat-pump installations is a trained and capable workforce, familiar with installing the technology in a range of installations. The MCS Heat Pump Standard, along with various manufacturer training schemes, has helped greatly in recent years. In the UK, the building industry is still in a period of transition, whilst it embraces demands to reduce energy. The heating industry is still learning how to adapt to the many changes it encounters and as such there are occasionally poor installations that perform badly, attract negative publicity and give the industry as a whole a bad name. In countries where there is a much greater market penetration of heat-pump technology, few installations fail to provide both financial and environmental benefits.

With present awareness of climate change and the need to conserve energy resources, it seems that heat pumps will have many roles to play as the future unfolds. There is no doubt that the heat pump is here to stay.

HEAT PUMP EFFICIENCY

Heat pumps have been around for many years. This rather mystical device promises to deliver 3kW of heat for every kW of electricity consumed.

Around the year 2000, when heat pumps were finding their feet, there were many poorly installed and poorly operated systems. however, twenty years on and we are now on our feet. There is no doubt whatsoever that there are many systems running with very low running costs. many systems have been monitored telling us that some can produce on average 3.5 to 4.5 kW of heat output for every 1kW electrical input with a well-installed heat pump applied well. Let us not get carried away here though: high-temperature applications, and/or lower cost systems will give lower numbers.

Planning an Installation – Things to Consider

Prior to deciding if a heat pump is right for you or not, you should be aware that there are many ways of reducing your energy expenditure. Most of these will involve capital outlay and the principle of ‘opportunity cost’ may be important here, since there is rarely an unlimited budget. If you spend on one option, you cannot afford another, so a choice between different options must be made. For example, you could choose between high-specification external thermal insulation and a new boiler, or a heat pump and cheaper insulation (assuming each option costs the same). The choices must be weighed up with respect to predicted savings in the long- and short-term.

Since there are many routes that could be taken, it is useful to consider things in this order:

1.Minimizing your energy demand.

2.Producing heat more economically and environmentally.

Reducing energy demand is always the best starting point. There are many factors that may affect your energy needs, such as the number of occupants in the house, their ages, how warm it needs to be, whether it is occupied all day and so on. Your overall energy strategy should start with trying to minimize the overall energy requirement. All the basic rules of energy conservation should be observed and there is plenty of advice about this available. Insulation is nearly always a prime option, even if it is very expensive. It should last indefinitely and should not require any attention. But there is sometimes a limit to levels of insulation that can be achieved, e.g. losing wall space due to internal insulation might be unwelcome and external insulation might be impractical.

Once your heat needs have been assessed, the method of heating (potentially a heat pump) can then be considered. Some people install a heat pump for environmental reasons and as an investment for the future, others are more concerned with their immediate running costs, so different people will have different concerns. Generally though, everyone will want the highest energy efficiency for the least installation upheaval and cost.

The following list suggests some initial questions to consider:

■Will a heat pump be suitable for my house and lifestyle?

■What different heat pump options do I have?

■What will a system cost to install?

■What RHI income could I receive, and over how many years?

■What are likely long-term running costs?

■How disruptive will the installation be?

■What CO₂ savings will I achieve?

■What else could I do instead?

You should be aware that only Microgeneration Certification Scheme (MCS) accredited installations attract RHI income. The vast majority of installers will be registered on the scheme.

A word of warning: it seems the norm for manufacturers to make exaggerated and highly biased claims for their products, and there are many one-sided websites. This can apply to all products. Double-check your research from multiple sources.

We hope that this book will answer these questions in an unbiased way.

Do use the index and glossary for clarification of terms.

Table of contents

• Cover
• Title
• Copyright
• Contents
• Introduction
• CHAPTER 1 - HEAT PUMPS IN CONTEXT
• CHAPTER 2 – UNDERSTANDING HEAT
• CHAPTER 3 – THE PRINCIPLE OF HOW A HEAT PUMP WORKS
• CHAPTER 4 – METHODS OF PUMPING HEAT
• CHAPTER 5 – EXTRACTING HEAT – THE SOURCE
• CHAPTER 6 – UTILIZING THE HEAT
• CHAPTER 7 – HEATING HOUSES
• CHAPTER 8 – ENERGY EFFICIENCY OF HEAT-PUMP SYSTEMS
• CHAPTER 9 – THE CONTROL SYSTEM
• CHAPTER 10 – ENVIRONMENTAL ISSUES
• CHAPTER 11 – ECONOMICS AND GETTING A SYSTEM INSTALLED
• CHAPTER 12 – TYPICAL INSTALLATIONS – CASE STUDIES
• CHAPTER 13 – COMMON MYTHS AND MISCONCEPTIONS
• Appendix I COPs of Ground Source
• Appendix II COPs of Air Source
• Appendix III Real-Test Data of Air Source
• Appendix IV What Goes on Inside a Heat Pump
• Useful Information
• Glossary
• Abbreviations and Useful Websites
• Index