Sustainable Homes of the Future: Heating

Current Heating Consumption of the United Kingdom

Historical Heating Demands of the UK (how we used to heat our homes)

Using data from the UK governments ECUK, we can see that the net domestic space and water heating consumption has only increased by less than 7% since 1970. Note that this is despite an estimated population increase of almost 20%. Further to that, it’s actually decreased since its peak in the early 2000s.

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Breaking this down further, space heating consumption has increased, though it has almost been counterbalanced by the consistent and steady decrease in energy going to water heating. However, it’s not just the raw amount of energy that we use to heat our homes that has changed, the methods have changed too.

Note: kWh is 1 kW of power drawn for 1 hour. This is slightly less than the energy required to run a kettle for 1 hour, or about the 1/75th of the battery capacity of a Model 3 Long-range. 1TWh is 1000000000 kWh (1×10^8 kWh).

Traditionally, homes were heated with fireplaces. Despite fireplace heating being a major breakthrough at the time, it’s not a particularly efficient way of heating a building. First off, it produces smoke, thus requiring a chimney for ventilation. This takes up space in the house. Secondly, it only heats the space that it’s in, not the whole house. This is ideal for very small houses or houses where the occupants spend the majority of their time in one room, but less than ideal. Despite these drawbacks, many people still use fireplaces today due to their homely appeal, generally in conjunction with a central heating system.

Eventually, most people in Britain settled on using boilers, typically oil, gas, or LPG at a pinch. These provide steady heat which can warm the whole house through, meaning we’ve stuck with them for several decades.

Current Heating Demands (how we heat our homes)

Presently, the vast majority of houses in the UK are still running on oil or gas boilers, though most are gas now. These function in much the same way as old oil or gas boilers, but they are considerably more efficient (usually above 90%).

Put simply, a boiler combusts gas to water, which is then pumped around the house electrically. Once it’s passed through the radiators in the house, it’s cold again, so the boiler reheats it. This cycle repeats for as long as is necessary to heat the home to the temperature set on the thermostat.

For a long time, this has been considered the best way to heat our homes. It provides consistent, stable heat that can be turned on within 20 minutes or so of it being requested.

How much energy should we spend on heating in the future? (how we should heat our homes)

So gas boilers are great, right? Well, sort of. Unfortunately, just in case the name wasn’t a giveaway, gas boilers burn gas. The problem is that this process can only ever be a maximum of 100% efficient i.e. all of the gas put into the boiler is being converted to heat, leaving no wasted energy. To give gas boilers credit, they’ve got pretty close to this efficiency, with many reaching over 90% now.

In order to get an increase in the efficiency of our heating systems, we’ll need to use different technologies. We’ll get to that later. Another solution would be to reduce the leakiness of our homes by better insulating them.

Assuming that these solutions are applied appropriately, what would be a heating demand goal that we could get to in the future?

We currently use around 6000 kWh per person per year to heat our homes. Let’s suppose that we wanted to halve that to 3000 kWh per person per year. That’s a completely feasible, (albeit a little challenging) target, especially considering that we have a lot of houses at the moment which would need significant upgrades.

How can this reduction be made?

Passive (no energy) Solutions

Introduction

Passive solutions can be put in place once, and just work for the rest of their lifetime. They require no energy, and not a great deal of maintenance. None of these solutions will physically heat our homes or our hot water, but they will go a long way to keeping them warm once they are heated up.

Here are some examples of passive measures we can take to reduce the amount of energy we use to heat our homes:

Insulation

In order to reduce the amount of energy spent on heating our homes, we need to make sure of the following:

  • Our homes aren’t losing heat unnecessarily
  • Our homes are effective at gaining heat when it’s available

The best way to avoid losing heat is insulation; both in walls and windows. The rate at which heat is lost through a wall is governed by the following factors:

  • Depth of the wall (i.e. distance from inside to outside)
  • Material type (e.g. stone, brick, insulation, plasterboard etc…)
  • Temperature gradient (if it’s hot inside and cold outside, more heat will be lost than if the temperature on both sides is roughly equivalent)
  • Surface area (more external wall area, more heat loss)

Insulation is not expensive, and many countries are insulating new homes extremely well. A number of different approaches to insulating both new and old homes could be applied in the coming years. For example, there could be a monetary incentive to insulate particularly leaky homes. Alternatively, stricter legislation could be introduced that forces developers to meet a certain maximum leakiness level.

How Insulation Keeps Your Home Cool and Warm - A-1 Guaranteed
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Loft insulation can provide the most benefit to the leakiness of a home.

It’s not just walls that need insulating though. Since hot air is less dense than cold air, heat rises. As a result, the roof is often a major source of heat loss, so loft insulation is necessary. Finally, windows can be double glazed, or even triple-glazed to prevent heat loss.

In terms of gaining heat from the sun in the first place, strategically placed windows are perfect for this. Buildings can be designed such that they collect enough heat to keep them warm, without collecting so much that they overheat.

Lifestyle

You may be wondering why I’ve placed lifestyle under the ‘passive solutions’ heading. Surely you would have to make a conscious effort to reduce the heating consumption of your home, right? Not necessarily. Once lifestyle changes are integrated into a routine, they become passive. They don’t really require additional effort or decisions.

For example, leaving your thermostat on a couple of degrees lower than usual can decrease heating consumption by up to 5%, whilst dropping it 5 degrees at night can reduce consumption by up to 10%. That means a 10% reduction on your energy bills. After all, the optimum sleeping temperature is somewhere in the region of 18 or 19 degrees. Furthermore, it has many other interesting benefits too, such as prolonged fridge and freezer lifespan, and even weight loss.

Hive Active Heating and Hot Water Thermostat | Insulation ...
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Smart thermostats, such as those from Hive, can help reduce heating consumption.

Other lifestyle changes include:

  • Reducing the time spent in the shower
  • Reducing the temperature of your shower
  • Choosing only to heat the rooms you are using, for example by using smart TRVs (thermostatic radiator valves)
  • Turning your thermostat and hot water off whilst you’re not home (note: make sure you keep your house at a base temperature above freezing to prevent water from turning to ice)
  • Use more water-efficient appliances, such as washing machines and dishwashers that are rated A+, A++, or A+++.

Design and Landscaping

The design of your house, as well as the landscaping around it, can have a significant impact on the amount of energy that is required to heat it.

For example, the sun spends the majority of its time shining towards the south side of houses everywhere in the world aside from the south pole. By placing lots of windows on the south side of the house, it gains lots of heat during the daytime but can get too hot in the summer. That’s where landscaping comes in.

Trees can be strategically planted around the property to provide it shade from the harshest sun of the day. Deciduous trees, which lose their leaves in the autumn, are particularly useful as they provide more shade in the summer than they do in the winter, effectively acting as an automatic temperature regulator.

Active (energy) Solutions

Introduction

Active energy solutions require energy but can have more of an effect on the temperature of the home than passive heating systems. An example of an active solution would be a traditional gas boiler. It takes the energy from burning gas and uses it to heat the home.

Active solutions typically have a greater impact on the environment than passive solutions, especially when being manufactured. However, many can either run off renewable energy sources like the sun or be fed by external renewable resources like a renewable electricity grid.

Air Source Heat Pumps

The future of heating our homes is likely to be in the hands of the heat pump. In fact, we’re already using them to cool our homes in the form of air conditioners.

The basic principle of a heat pump is to move the heat from one area to another. In the case of air conditioning, the heat is moved from inside the home to outside the home, cooling the inside of the home down and heating the outside of the home up.

The heat pump has one key advantage over gas boilers. In addition to it running off of electricity, which can be obtained from renewable sources, it uses considerably less energy to move/generate the same amount of heat as the gas boiler. This is because it’s efficiency is very high. In fact, whilst gas boilers can be up to 100% efficient, heat pumps can be up to 500% efficient, meaning for every watt of power supplied, it can move 5w of heat. That makes the gas boilers 1w seem archaic.

There are a few types of heat pumps, but air source heat pumps are typically the easiest and cheapest to install as they only rely on a source of fresh air.

Typically, air-source heat pumps come in two types: air to air, and air to water. Air to air is just like an air conditioner, blowing cool air into the room. Air to water functions more like a traditional central heating system, by taking the heat from the air and using it to heat water, which then passes through radiators and heats the home.

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Ground Source Heat Pumps

Built on the same principles as air source heat pumps, ground-source heat pumps deliver the same (or greater) efficiency benefits but do come at a greater cost.

This is because, during installation, large holes must be dug in the ground to lay pipes. Why go underground? Well, once we go below the surface of the earth by just a few metres, the ground doesn’t really care whether it’s summer or winter and is approximately the same temperature all year round. As we dig slightly deeper towards the mantle, the crust starts to get hotter, to around 70˚.

We then lay pipes into these holes and pump water down them and back up again. On its journey, the water absorbs some of the heat from the ground, heating it up to 70˚. You can see where this is going. The ground is acting as a boiler.

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Minimal energy is required to run the pumps, meaning the efficiency of ground source heat pumps is similar to their air-source counterparts.

So, why use ground source heat pumps instead of air source?

Air source heat pumps work best when there is a small temperature gradient. That means the temperature inside is roughly the same as the temperature outside. However, their efficiency really drops off when the temperatures drop below 10˚C.

Now, remember what I said about the ground not caring about the seasons. Ground source heat pumps function equally well (almost) anywhere in the world. Hence, if you live in an extreme climate, ground-source is the way to go.

An additional advantage of ground source heat pumps is economies of scale. Larger boreholes can be made to supply larger numbers of houses. For example, a new housing estate could have a borehole which supplies all of the houses on it.

Solar Thermal

One particularly efficient method of heating our hot water is to use solar thermal heating. Whilst solar thermal panels can be used to generate electricity, they are more efficient when the energy gathered from them is used directly as heat, for example in a shower or hot water heating system. In principle, solar thermal panels concentrate the sunlight, heating a fluid. This fluid may be water, oil, or others.

http://glenergysolar.ie/wp-content/uploads/2015/10/Solar-Space-heating-installation.jpg
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In comparison to solar photovoltaic panels, they’re considerably more efficient at converting the sun’s energy to the desired form, be that heat or electricity. Solar thermal panels are approximately 65% efficient at converting the sun’s radiation into heat, whereas most solar PV panels are around 15-20% efficient at converting radiation to electricity.

For most, a mixture of solar PV and solar thermal would be optimal. Solar PV can be used to generate the household electricity, and excess can be sold off for revenue. Solar thermal can be used to provide hot water.

Conclusion: Reducing our heating consumption

With all these new and efficient technologies, the question of ‘why do we need to reduce our heating consumption in the first place’ may arise. It’s a good point. If we can make our heating sources net neutral or net positive, why bother reducing our consumption?

Currently, it’s very difficult to manufacture such technologies without damaging the environment. For example, solar PV panels often include toxic chemicals, which may cause damage to the environment if not disposed of correctly.

As a result, the future will comprise of two things; making our heating sources cleaner, and reducing our heating consumption. Passive solutions will allow us to reduce our consumption, active solutions will allow us to make our heating sources cleaner.

References

Energy Saving Trust. (2018). Air source heat pumps vs. ground source heat pumps. [online] Available at: https://energysavingtrust.org.uk/air-source-heat-pumps-vs-ground-source-heat-pumps/ [Accessed 13/12/2020]

Green Coast. (2019). Solar Thermal vs Photovoltaic Solar: What is the Difference?. [online] Available at: https://greencoast.org/solar-thermal-vs-photovoltaic/ [Accessed 20/12/2020]

Leblanc, R. (2019). What is the Environmental Impact of Solar Power Generation?. [online] Available at: https://www.thebalancesmb.com/what-is-the-environmental-impact-of-solar-power-generation-4586409 [Accessed 20/12/2020]


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