The cheap­est way to heat wa­ter

Hot wa­ter heat­ing is re­spon­si­ble for at least 30% of the av­er­age NZ home power bill. When you con­sider heat pump wa­ter heaters can turn 1kWh of elec­tric­ity into 3kWh equiv­a­lent of hot wa­ter – it’s by far and away the best way to slash your power bills.

Element - - Element Promotion - In­ter­view: Dana Dar­win En­ergy Al­ter­na­tives NZ Ltd

Dana Dar­win is founder of af­ford­able en­ergy com­pany, En­ergy Al­ter­na­tives. A trusted ad­vo­cate for ef­fi­cient en­ergy tech­nol­ogy and a proven leader in the NZ so­lar sec­tor, Dana be­longs to SEANZ, SANZ, the NZ Green Build­ing Coun­cil, and the Sus­tain­able Busi­ness Net­work.

How do heat pump wa­ter heaters work?

Heat pump wa­ter heaters use elec­tric­ity to move heat from the air to the wa­ter in the tank in­stead of gen­er­at­ing heat di­rectly via an el­e­ment.

The prin­ci­ple is sim­i­lar to a re­frig­er­a­tor but in re­verse, gen­er­at­ing heat not cool­ing. Highly ef­fi­cient, a good heat pump wa­ter heater (HPWH) is three to four times more ef­fi­cient than con­ven­tional elec­tric wa­ter heaters (an av­er­age one is 2 – 3 times more ef­fi­cient).

There are two main types; ‘all-in-one’ (in­te­grated) sys­tems or ‘split’ sys­tems.

An all-in-one sys­tem has the heat pump at­tached to the top of the stor­age tank and is a good op­tion when ren­o­vat­ing, build­ing new or re­plac­ing your old hot wa­ter cylin­der. With a ‘split’ sys­tem you can keep your old tank, pro­vided it’s not too old, and the HWHP is at­tached to it.

How fast is the in­dus­try grow­ing

Global sales of HPWH are in­creas­ing strongly and both the US and China re­port 13% a year growth.

Here in NZ the in­dus­try is steadily grow­ing with in­creased con­fi­dence in the per­for­mance of the prod­ucts as a re­sult of an EECA sub­sidy pro­gram, and favourable re­ports from Con­sumer Mag­a­zine, BRANZ and the Par­lia­men­tary Com­mis­sioner for the En­vi­ron­ment.

Do you fore­see a time when all new builds will in­clude a HPWH?

House­holds with moder­ate-to-high hot wa­ter us­age, eg four per­son families, are very well suited for HPWH so, yes, I ex­pect that in time all new builds will in­clude them. I also ex­pect HPWH to be­come stan­dard in new builds for mul­tiu­nit prop­er­ties like mo­tels, ho­tels and re­tire­ment vil­lages.

Heat pump wa­ter heaters do cost more at the out­set than a tra­di­tional elec­tric wa­ter heater with an el­e­ment. Smaller house­holds us­ing very lit­tle hot wa­ter are un­likely to get enough en­ergy sav­ings to re­cover that ini­tial cost and are pretty well served by con­ven­tional elec­tric wa­ter heaters.

Is a HPHW the most eco-friendly of wa­ter heat­ing de­vices?

A good heat pump wa­ter heater will trans­fer three times as much heat into the wa­ter as elec­tric­ity used. This ef­fi­ciency means you’re us­ing 66% less elec­tric­ity to heat your wa­ter. Since NZ’s elec­tric­ity is 70% re­new­able, the non-re­new­able en­ergy con­tent of the heated wa­ter is less than 10%. No other wa­ter heater can match this, in­clud­ing so­lar wa­ter heaters which use pro­por­tion­ally more elec­tric­ity dur­ing the win­ter months when the non-re­new­able pro­por­tion of elec­tric­ity gen­er­a­tion is high­est.

The less elec­tric­ity we use, the less we are con­tribut­ing to pol­lu­tion and cli­mate change, mak­ing HPWH units bet­ter for families and our en­vi­ron­ment.

Av­er­age price of a HPWH?

All-in-one sys­tems, which in­clude the tank, cost between $2400 and $4500, plus in­stal­la­tion, (typ­i­cally between $750 and $1500). If you ex­clude what you’d spend any­way on a stan­dard hot wa­ter cylin­der, plus the plumb­ing and elec­tri­cal labour, the ex­tra cost of a heat-pump wa­ter heater is between $1000 – $3000. This ex­tra cost is rapidly re­cap­tured due to the high ef­fi­ciency and cost sav­ings of the unit.

“A good heat pump wa­ter heater will trans­fer three times the heat into the wa­ter than it uses in elec­tric­ity.”

What is the ex­pected re­turn on in­vest­ment (ROI)?

The ROI de­pends upon the ex­tra cost of the sys­tem and in­stall and the quan­tity of hot wa­ter be­ing used in your home.

In a retro­fit, where an ex­ist­ing tank needs to be re­placed, or the hot wa­ter sys­tem is be­ing up­graded to mains pres­sure, the mar­ginal cost is around $800-$1000, which can pro­vide a pay­back of 18 months to two years.

For a new build, the pay­back pe­riod can be 1 – 3 years for a fam­ily of four or more. An an­nual en­ergy sav­ing of $600 – $700 is read­ily achieved, and can in­crease by $200 – $300 per ad­di­tional res­i­dent.

The mar­ginal re­turn for a fam­ily of four that in­vests in a HPWH when ren­o­vat­ing or build­ing a new home can range from 40 – 60% per year. A strong re­turn on in­vest­ment worth con­sid­er­ing!

Do HPWH units work well with a so­lar PV ar­ray?

If the fam­ily has, or in­stalls, a so­lar pho­to­voltaic sys­tem, the two tech­nolo­gies com­ple­ment each other very well, and work par­tic­u­larly well in house­holds where the main hot wa­ter de­mand oc­curs dur­ing the morn­ing.

Set­ting the HPWH to op­er­ate dur­ing sun­light hours to co­in­cide with when the so­lar PV can pro­vide the power al­lows for the wa­ter tank “bat­tery” to store the en­ergy for later use.

A HPWH can im­prove the re­turn on the so­lar power in­vest­ment from 10% to 30% per year, be­cause hot wa­ter heat­ing makes up so much of house­hold power bills.

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