Heat pumps and other ‘new’ systems are beginning to look attractive, but they often only make sense as part of a wider overhaul, writes
The prospect of home improvement, extensions and serious renovations should by now be understood to be as much about energy efficiency as it is about square metres of glittering architecture and aesthetics.
Simply plumbing and wiring in a new heating source (adding a new gas or oil boiler or an air source heat pump/ASHP) is not something most of us should do in isolation.
That new heat source should be part of a raft of improvements to optimise the building’s entire energy performance.
When interviewing Cork architect Loic Dehaye recently, I was surprised to see he had vouched for a natural gas condenser boiler in his renovated 1950s Cork home, rather than a heat pump (HP).
His argument, (worth remembering) is that if you get the structural, insulation ventilation and heat delivery elements of the house right, future swaps to say a HP from sole gas boiler heating, are a relative plug and play.
Right now, natural gas, despite the threat of carbon taxes, remains a clean, convenient cost-efficient performer for urban grid dwellers.
The really good news is that natural gas will soon be joined (injected is the trade term) by renewable gas usage (biomethane from on-farm anaerobic digestion). Run through the Irish national gas grid, this has the potential to supply as much as 50% of our domestic need by 2050.
Between HPs powered in part by on-roof photovoltaic arrays (PV) and entirely green gas, our carbon performance could be set for a vast improvement.
Even where highly-efficient natural gas is available for home heating, warming water, running the dryer and more, a new build or very deep renovation seems to indicate the inclusion of a grant-aided heat pump (ASHP generally).
At their very best, with an array buried in the earth, for every single unit of electricity put into an HP, 3-4 units of thermal energy (kWh) can be returned to the house.
Real-life running costs can vary wildly and leave customers without home generated wattage at the mercy of national electricity prices. At €8-€12,000 installed before grant aid, are HPs right for every retrofit?
“Heat pumps are an attractive choice,” says Barry Gorman, sales technician with leading Irish boiler manufacturer and supplier Grant.
In the majority of situations, they are very quiet, clean and sit neatly outside a property. For those looking to install an ASHP system, they need to keep in mind that unlike oil or gas boilers that run at 60-70°C, heat pumps work best at a flow temperature of around 30-45°C.
Emitters including radiators and underfloor heating have to be suitable to operate at these lower temperatures. Additional work could be required with a heat pump to upgrade emitters and insulation too.
“Changing an oil or gas boiler to a more modern version can be a relatively straightforward process. However, in any renovation situation, homeowners should always be looking at how they can improve the fabric of their building toreduce heat loss, so this is where it can be slightly more demanding.”
Changing from a conventional oil or gas boiler to reliance on an electrically powered heat pump that sips warmth from the air? That’s quite a leap of faith for some homeowners. However, hybrid systems (as with cars using petrol and electricity) are available.
“Hybrid allows home-owners to enjoy the benefits of fossil fuel and renewable technologies as it combines our patented Vortex condensing oil technology with an Aerona3 monobloc air source heat pump,” says Barry.
“Generally, it is aimed at large new builds and houses with large heat load demands. It also means that you can stay on single-phase electricity. This is important because if you were a homeowner with a large property and wanted to use heat pumps, you may need two or three heat installed, requiring a three-phase electricity supply - not always available or economically viable.
“Consider a 250m square home built around 10 or more years ago that has a heat demand of 20kW. Generally, with exterior temperatures of 5°C and above, the heat pump will do all of the work. From 5° down to -4°C, the heat pump will still run, while the oil boiler will assist with the alow-temperature flow.
"If temperatures drop to below -4°C, the oil boiler will take over completely, but on average, the heat pump will supply 80-90% of the heat required throughout the year.”
Gas fired heat pump hybrids are also now available as an alternative to electric HPs. Find out more at gasnetworks.ie. Daiken also does a model that combines a gas boiler with an electric heat pump — the Altherma, energywiseireland.ie.
With the Sustainable Energy Authority of Ireland (SEAI) having killed grants for oil condensing boilers, are they really still part of the conversation as we try to decarbonise our energy sector, including home heating? Barry argues that, yes, oil condensing boilers with 97% efficiencies are still a good choice, but only for some houses.
“In a lot of cases in Ireland, people do not have access to natural gas or do not have the resources to upgrade their heating systems for an air-to-water heat pump. With a condensing oil boiler, the flow temperature can go up to 75°C, suiting conventional radiators, fan-assisted convector radiators and underfloor heating.
Oil boilers have an attractive price point, are straightforward to install, and are a proven technology that is extremely reliable. In some situations, installing a heat pump may be counterproductive as the homeowner could end up spending a prohibitive amount of money on electricity to run the heat pump.
The boiler is a start, but modern heating controls are key, he says. “All oil boilers have a thermostat, however, it doesn’t give any indication of how hot or cold your house is. With modern thermostatic controls, you will be able to set the desired temperature throughout your home, say 21°C for example.
“If your heating is scheduled to go on for an hour in the morning and an hour in the evening, the thermostat will gauge when it reaches your desired temperature and will turn off. On a morning of mild weather, it may only take 20 mins to reach 21°C, whereas on a colder winter morning it could take the full hour. Without such heating controls your heating system could be burning away for an additional 40 minutes.
“Modern heating controls can also facilitate zone heating, meaning that homeowners can choose the specific areas of the home that they wish to heat. Such controls really help homeowners be much smarter about their energy usage.”
Always-on heating is something many of us are unfamiliar with. “Another advantage we find with the air source heat pump is that it has the potential of running up to 24 hours. This ensures that your home is at a constant ambient temperature of 21°C and has domestic hot water at all times. The overriding advantage here is comfort-heat as opposed to just periods of warmth or cold.”
Where economic natural gas heating is not available or where a sustainable choice is wanted there’s also biomass heating for both space heating and in a fully automated system pellet fed or wood gasification boilers.
“What hurt the wood pellet industry was the cost of oil and gas products,” says Barry.
The fuel costs were generally on par with one another over the past few years. However, the capital costs of the technology is more expensive, so it can be hard to convince homeowners to go that way.
“Biomass heating should always be on the table for consideration by those that are building a new home or retrofitting. To future-proof a home and steer away from fossil fuels, wood pellet technology, it’s a strong choice as it requires very little change to existing plumbing.”