Global Warming Effects (updated 2011)

Vast amounts of heat energy are used for heating our houses, and it is always advantageous to minimise the heat requirements by normal conservation measures like insulation. This is certainly the best and simplest first-step. Sadly, we cannot all live in super-insulated eco-houses, so significant amounts of heat energy are required.

Any use of fossil fuel creates harmful CO2 emissions. Electricity is mostly produced by burning fuels, and the process of generation is inefficient. Electricity is therefore not a good form of energy for heating. However, the energy-advantages of heat pumps can, in most cases, more than compensate for this, and makes them score well with respect to CO2 emissions.

Note: The assumption that you can sign up to 'green' electricity and become 'carbon neutral' has not been made since electricity all comes from the same 'pot'. However, it is clearly an advantage to buy electricity from a genuine supporter of lower-carbon generated electricity.

The nation's mix of electricity-generation methods results in different levels of CO2 pollution. Coal power stations are not good, modern gas power stations are much better, hydro and large scale wind power produce almost no CO2 (even when all the energy to build them is accounted for).
The 'mix' of generation leads to a figure that is published at:-
Click>>> Ecotricity website and Realtime Carbon. Its well worth a look.

The official average figure used for UK electricity generation is currently being debated.The official figure has been 0.422kg CO2 per kWh generated. This allowed for some projection into a lower-carbon future, and the current actual figure is on average around 0.5. However, according to SAP 2009 the figure is now 0.517 kg CO2/kWh. It is unclear if the UK will meet its predicted targets. No doubt the figures will continue to be debated. However, it is almost certain that electricity will get cleaner in the future, and these figures will reduce over the lifetime of a heat pump installed now.

The graph compares the carbon dioxide emissions of common heating systems (gas, oil and electricity) to that of heat pump systems. The COP (efficiency) for a typical Ground Source heat pump with radiators is around 3, but if well designed underfloor is used the efficiency can be 4. It could however be as low as 2.5, or even less, for a poorly designed system.
I have taken a figure for electricity as 0.5 which is our UK presentt actual average.

Notes and assumptions.
Gas condensing boiler efficiency 88%
Oil boiler efficiency 87%
LPG condensing boiler efficiency 88%
Wood varies from 0 to 0.06 depending on processing, transportation and burner efficiency.
Electricity 100% efficient at point of use. Off-peak use is less efficienct due to warmer average house temperature, however, electricity is generated 'cleaner' at night.

As can be seen, the carbon dioxide contribution from a good heat pump system can be 1/2 that of oil or LPG. Direct electric heating, especially storage heaters, scores very badly with respect to global warming.
Wood burning is likely to show the lowest CO2 figures but this depends on how it is burnt, and where the wood is sourced from. Locally collected logs are carbon neutral, but processed pellets and chips require energy to make. Currently some wood fuels are imported.

Many heat pumps incorporate a normal electric top-up heater to cope with the coldest periods in the winter. This is more the case with air-source systems since the period of highest heat-demand also corresponds with the time when there is minimum heat available in the air. Therefore, on the coldest day the electricity consumption for some heat pumps will increase many fold, putting a strain on the electricity supply grid. It would be better to use boilers, or ideally, wood stoves as a back-up. It should however be noted that the total annual contribution by top-up heaters is surprisingly small.

The COP (coefficient of performance) of a heat pump is the ratio of input to output.
Fuel figures SAP 2009.

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The Graph below might be useful when assessing the benefit of running a heat pump. (its not as complicated as it looks!)

The vertical scale on the left shows CO2 pollution per kWh of useful heat (allowing for losses). The two horizontal lines show figures for mains gas and oil heating. The curves are for heat pumps with COP's up to 5. Direct electric heating has a COP of 1, and this is shown on the left.
The UK government figure for CO2 pollution caused by electricity generation has been 0.422 (kg co2/kWh). However SAP 2009 lists it at 0.517 (kg co2/kWh). The actial present figure is around 0.5, and will tend to be high in mid winter when coal power station are brought on-line to meet increased electricity demand, and lower at night when the percentage provided by nuclear is high.
Given current figures of 0.5, it is necessary to have a COP of about 1.7 to equal the pollution caused by oil heating.
You can use this graph to decide if its better to run your heat pump or your gas boiler depending on your systems COP, and the figures for mains electricity.
The blue line represents the future when the electric grid becomes de-carbonised. At this point, heat pumps will come into their own.

Click below for some amazingly useful tools that gives actual UK generation CO2 figure
Real time carbon
Ecotricity

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REFRIGERANTS (the working fluid)

Gone are the days of refrigerants affecting the ozone layer. They are now all 'ozone-friendly'. However, most refrigerants do have a high global warming potential, meaning that they are far more potent than the gas - CO2.

The refrigerant fluid within the heat pump is very unlikely to leak (when did you last hear of a refrigerator leaking its refrigerant?) but should it do so, it could detract from the CO2 savings. The following information attempts to give a balanced view of the issue and concludes that the savings made during the heat pump's working life, far outweigh any negative effects caused by loss of refrigerant.

The following table lists the Global Warming Potential (GWP) of various gases. This gives a figure of how damaging the gas is, as compared to CO2.

Refrigerant	Global Warming Potential
Carbon Dioxide, CO2	1
Hydrocarbon, HC	7
HFC R407C, R410A, R134A	1,900

Inside a typical 8kW heat pump there is approximately 2kg of HFC refrigerant. This should stay intact within the unit for its whole life. It is a legal requirement to recover the refrigerant charge at the end of the heat pumps life. This can then be used in another heat pump, or destroyed.

In this worse case scenario, we have assumed that the refrigerant is lost via a leak during a 10 year period.

The first five columns show the total CO2 released to atmosphere over the 10 years of running each system. The saving in CO2 that you would make if you have a heat pump would be the difference between the heat pump column (purple), and the fuel it replaces to the left.

The common HFC refrigerants (shown in pink) have a relatively small effect compared to the vast amount of CO2 produced by using energy over a long period.
Like your domestic fridge, a heat pump is unlikely to lose its refrigerant charge over its life, so this column could prove to be very small in reality.

Graph taken from expected consumption for a year 2002 regs. house.
10,500kWh space heating, 3,600kWh. hot water.

Whilst this might show that HFC refrigerants are acceptable, it is obviously preferable to use an Hydrocarbon (HC) refrigerant if possible. If heat pumps become widespread, then benign refrigerants like hydrocarbons should ideally be adopted.

We have added wood to the graph to indicate how good logs are as a back-up for a system.

Notes and assumptions
Gas condensing boiler efficiency 88%
Oil boiler efficiency 87%
Electricity 100% efficient at point of use
Heat Pump COP 3.8 (i.e. 2.1 kW input for 8kW output).