Thinking big about heat pumps
Is the belief that heat pumps can only deliver low flow temperatures holding back their use? Dave Pearson of Star Renewable Energy certainly thinks so.
It is well documented that generating electricity consumes 25% of our nation’s fuel and that transport is responsible for 25%. Less well known is that heating accounts for 50%. That's half of a total energy bill of £32 billion a year — much of it imported in exchange for currency.
Whilst some processes will invariably remain best suited to combustion, such as distillation or steam production, much of the £16 billion used to generate heat is simply to heat buildings to 21°C and water to above 50°C.
Is it really necessary to burn stuff at over 1000°C to heat buildings and water?
As has been proven for decades using heat pumps, the answer is a technical ‘no’ but a commercial ‘maybe’.
Heat pumps were widely used in Switzerland during the Second World War Switzerland to harness hydro-electricity when fossil fuels were being commandeered elsewhere.
Following the OPEC oil crisis in the 1970s, some far-sighted regimes in Scandinavia, in particular, realised that the solution proposed by Lord Kelvin in 1852 that can halve the dependence on fossil fuel might be viable technically and commercially.
It really boils down to the ratio of gas to electricity costs per kWh (including inefficiency). Markets and tariffs are skewing this analysis right now, but digging a bit deeper...
Suppose we have 10 units of gas.
We can burn them in a boiler and get around 8.5 units of heat.
Or we can generate electricity in a modern combined-cycle gas-turbine plant with delivered output of around 5 units of electricity.
Modern heat pumps in a well designed and, more crucial, well operated (more of that later) installation could deliver four times as much heat as electricity consumed.
So in our simplistic model, we started with 10 chocolate buttons and now we have 20. Even a 3-year-old would understand that.
So where can we harvest heat, and how best can we use it?
The UK has a boring climate:
• three weeks of summer;
• three weeks of winter;
• 46 weeks of sprautumn.
During that in-between period, we need both heating and cooling and have surface water resources such as rivers in abundant supply.
A river like the Thames with a flow rate of 200 000 l/s, if cooled by 2 K would yield 840 MW of heat — enough for around 300 000 houses. Better still, the heat output includes the electrical power input, so add half to a third more.
If you are not near a river, then look for a canal or flooded coal mine. Even an old gravel pit will be full of water that is rarely frozen.
What about sewage-treatment plants? A typical facility will be dumping nearly 100 MW, enough for 10 large hospitals or 20 universities and rarely below 9°C.
Look a bit further, and we have waste heat from power stations, data centres and, of course, industry. It is fair to say we can find heat in most locations.
But what about the classic observation: ‘We looked at heat pumps, but unless you have underfloor heating at 50°C they don't work.’
Wrong. Modern heat pumps are proven to be capable of at least 90°C in big facilities.*
They can certainly deliver over 70°C, even if the system has an output of only 500 kW.
It is time for the entire supply chain to recalibrate its ‘norms’.
Heat pumps do work and can reach even 90°C with an efficiency of 300%.
So what turns a good heat-pump solution into a great heat-pump solution?
Clearly getting the source and demand temperatures as close together as possible is a big step.
Most buildings are designed for peak heating delivered with 82°C water. This means on the oldest day, with the highest demand, the radiators need 82°C. We don't live in that climate; remember sprautumn?
In reality heat demand was overstated, and radiators are generally overspecified to have a degree of slack to protect the original designers.
Most heating systems will run at 72°C; the 82°C is to protect the boiler flue from condensation.
So get the source and demand temperatures as close together as possible. Even vary them from mild to cold days. We could call it ambient compensation.
There is nothing to prevent reverting back to 82°C and using boiler top-up if we experience a prolonged cold snap.
Every degree is worth 1.5% of running cost. Imagine a 15% saving just by managing the system better.
Other things we can do to optimise are remove the habit of night-time off followed by a 7 a.m. blast. The building fabric can act as a thermal store, and electricity is around 40% cheaper at night.
We can also programme the controls to avoid peak electrical demand (usually tea time). There are even bonus schemes regarding remote off positions. There are also bonuses for remote on when the grid has too much juice — better than paying a constraint payment to a wind-turbine farm.
Worth pointing out that an installation at Drammen in Norway modulates from 2 to 13 MW and delivers 85% of the annual heat requirement. Boilers are rarely used — not surprising as the heat-pump heat is 80% cheaper.
Heat pumps don't magic heat from nothing. They cool one bit and heat another. What if we configured society to match up heaters and coolers — such as houses and data centres? Then we could share the electrical cost and save even more.
Life isn't easy. But in this case of lower-carbon lower-cost heating, the effort is measured in jobs. Jobs for energy consultants, trench diggers, heat-pump manufacturers and maintenance teams.
A famous ice-hockey player once said, ‘You miss 100% of the shots you don't take.’
The Government has delivered the vision, the policy, the incentives and the pressure on the status quo.
Only a society that deserves higher bills, dirtier air and global climatic chaos would not step up and take a shot. It's a triple whammy gain for planet, people and profit.
Why isn't Westminster heated from the Thames?
Dave Pearson is a director with Star Renewable Energy.
