Heating more efficiently using Carbon Dioxide

Carbon dioxide is a bit of a villain when it comes to climate change.

Ecocute

But it may also be a climate saviour if we use it intelligently.

And that's thanks to a Norwegian and the inhabitants of another group of islands similar in size to the UK but further east. Much further east. The Japanese.

The Norwegian in question was Gustav Lorentzen a scientist working in the area of thermodynamics who rekindled interest in using carbon dioxide (CO2) as a refrigerant in heating and cooling systems. Between 1988 and 1991 Lorentzen developed something called the thermodynamic transcritical cycle and a new simple and efficient way of regulating CO2 systems.

A collaboration between Lorentzen and the Japanese company Denso followed and led to the development of new heat pump technologies based upon CO2.

So what?

Well, CO2 has some very useful properties when used in heat pumps.

The problem with most existing heat pump technology

Today, most heat pump technology makes use of hydrofluorocarbons (HFCs and HCFCs) as the working refrigerant. These heat pumps output hot water at a temperature of up to 45 or 50 degrees centigrade. This would be warm enough for hot water to wash with and to drive your heating system if you had an extremely well insulated house and under floor heating. But most people don't.

Most houses in Edinburgh are heated by gas and the output temperature of the water from the gas boiler around your heating system is usually about 70 degrees centigrade. You can oversize your radiators to increase their heat output, but you may have to replace all the pipework to your radiators if they are less than 15mm in diameter. Quite an upheaval.

The other problem with heat pump technology using HFCs or HCFCs is that every now and then you have to raise the temperature of the water in the system to 65 degrees centigrade in order to prevent Legionnaires' disease. And the temperature lift from 50 degrees centigrade to 65 is done using an electric immersion heater. Not very efficient.

And of course the performance of heat pumps using HFCs or HCFCs drops off dramatically when the outside temperature drops below +5 degrees centigrade such that at outside temperatures of -10 degrees centigrade, the system ceases to be a heat pump and uses built in immersion heaters. This is very inefficient.

The advantage of CO2

Heat pumps using CO2 can produce hot water at temperatures of 65 degrees centigrade without using an electric immersion heater. Some claim to be able to produce water at higher temperatures. This solves the Legionnaires' disease problem and allows existing pipework and radiators to be used. Simply replace your gas boiler with a CO2 heat pump system.

Heat pumps using CO2 also operate down to much lower outdoor temperatures. As low as -25 degrees centigrade.

The advantage of a heat pump using CO2 is that it operates as a heat pump over a much wider range of temperatures that match both the climatic conditions in Edinburgh and the majority legacy heating infrastructure (amongst other things - more on this in a later blog).

Ecocute

First UK Installation of SANYO's CO2 Heat Pump SystemJapanese manufacturers have been producing air source heat pumps using CO2 as a refrigerant since 2001. These units are often referred to as Ecocute units. The Japanese government has had an initiative to increase the efficiency of these units towards 500% and there are millions of installed units in Japan. The first Ecocute unit has arrived for sale in the UK, the Sanyo CO2 Eco air source heat pump.

Coefficients of Performance (CoP)

The efficiency of heat pumps is usually referred to as the coefficient of performance (CoP) rather than being expressed as a percentage. On a day with an outside temperature of 15 degrees centigrade the Sanyo CO2 Eco air source heat pump will produce water at 65 degrees centigrade with a CoP of 3.1. An electrical input of 1.6 kW is combined with 3.3 kW of free energy from the air to produce 4.9 kW of energy to heat water (4.9/1.6 = 3.1). Under some operating conditions, CoPs of 4.1 can be achieved by this unit.

On a cold day with an outside temperature of -5 degrees centigrade the Sanyo CO2 Eco air source heat pump will produce water at 65 degrees centigrade with a CoP of 2. An electrical input of 2.6 kW is combined with 2.58 kW of free energy from the air to produce 5.18 kW of energy to heat water (5.18/2.6 = 2.0).

The Sanyo CO2 Eco air source heat pump

There will be a presentation about this unit at the Energy Fair on the 5th September 2009. I shall be blogging further about this very significant heat pump in future blogs.