Innovative new home heat-seeker ain’t no run-of-the-mill drill

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Construction machinery that reduces home-heating costs is being used for the first time in New Zealand – near Arrowtown. 

On a construction site at Millbrook Resort’s Millbrook West is an $800,000 German-made ground source/geothermal-specific drilling rig, imported and owned by Christchurch firm McMillan Drilling. 

The rig is drilling 12 holes – each 100 metres deep – to source ground heating for an 850sq m house and two plunge pools. 

“It drills the hole, puts pipe in and then fills the hole with putty back up, and that conducts heat from the ground to the pipe,” Steve Jarvis, from Arrowtown installer Peak Plumbing, says. 

The ground water, which is a constant 10 degrees, is pumped around the holes, then goes to a heat pump machine in a plant room. 

A compressor in the heat pump squeezes the water, raising it to about 50 degrees. 

It’s then pumped through the underfloor heating in the house at about 41 degrees. 

Allowing for further heat loss, it then heats the house at 21 degrees. 

Jarvis says a test rig was placed over the first hole that was drilled to find out how many kilowatts of heat it will source. 

“We connect that machine to an internet line and send the data to the States.” 

The ground source rig is more accurate, two to three times faster than water-bore rigs formerly used and is guaranteed in any type of ground, Jarvis notes. 

“It looks as though it’s going to be pretty busy down here because we’ve just got another couple of jobs for it.” 

Jarvis won’t disclose the client or what it’s costing him. 

“Eventually, if we can get enough work, [the rig] will start getting cheaper.” 

The real savings come at the other end, Jarvis maintains. 

Heating a large house would cost about $6000 a year, down from about $20,000 for gas. 

“There isn’t a cheaper way to heat your house with central heating.” 

Jarvis estimates running costs for ground source heating are only five cents per kilowatt compared with 16c for gas, 12c for diesel and 10c for air to water heat pumps. 

“So a house with ground source will be 68 per cent cheaper to run than a gas boiler and 58 per cent cheaper than diesel.” 

For a 250sq m house using a rough average of 15,000Kw a year, the annual costs for ground source heating work out at about $900, Jarvis says. 

That compares with $1500 a year for a hot water heat pump, $1800 for a diesel system and $2400 for gas.
Installing ground source heating for a 150sq m area is about $35,000, Jarvis says. 

“Somebody who’s prepared to spend a wee bit more on the installation cost will get a cheaper running cost.”