Hot wa­ter heat pumps

Sales of heat pump wa­ter heaters are ex­plod­ing, thanks to a rep­u­ta­tion for be­ing the most ef­fi­cient and eco-friendly way to heat wa­ter.

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It ap­pears that the glory days of the trusty hot wa­ter cylin­der may be on the wane, bumped aside by its up­start young cousin – the heat pump wa­ter heater (HPWH).

We’re all fa­mil­iar with the heat pump space heaters, now ubiq­ui­tous through­out New Zealand as an ef­fi­cient, con­ve­nient and rel­a­tively cheap method of heat­ing our homes. The same tech­nol­ogy has now ar­rived with re­spect to hot wa­ter, with ex­cel­lent re­sults when your power bill ar­rives.

Glob­ally, sales of heat pump wa­ter heaters are the fastest grow­ing wa­ter heater. 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 Par­lia­men­tary Com­mis­sioner for the En­vi­ron­ment.

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

The work­ing prin­ci­ple is very sim­i­lar to a re­frig­er­a­tor

“An av­er­age HPWH is three to four times more ef­fi­cient than con­ven­tional elec­tric wa­ter heaters.”

but in re­verse, gen­er­at­ing heat – not cool­ing. An av­er­age HPWH is three to four times more ef­fi­cient than con­ven­tional elec­tric wa­ter heaters. Con­sider that 30% of the av­er­age power is ded­i­cated to heat­ing wa­ter, and do the maths.

There are two main types, an ‘all-in-one’ (or in­te­grated sys­tem) and a ‘split sys­tem’.

An all-in-one sys­tem has the heat pump at­tached to the top of the stor­age tank and a split sys­tem has the heat pump sep­a­rate from the tank – gen­er­ally out­side.

All-in-one sys­tems are avail­able for both in­door and out­door lo­ca­tions and are a good op­tion when ren­o­vat­ing, build­ing new or re­plac­ing your old cylin­der, whereas a split sys­tem can be retro­fit­ted to your ex­ist­ing tank pro­vided it is not too old.

Add it up

Heat-pump wa­ter heaters cost more at the out­set than a stan­dard elec­tric wa­ter heater. There­fore, they re­quire the ini­tial cap­i­tal cost to be re­cov­ered through en­ergy sav­ings, which is in pro­por­tion to the amount of hot wa­ter used by the pur­chaser. For house­holds with a low hot wa­ter us­age, it may well mean that your pay­back pe­riod is sim­ply too long and you’re bet­ter served by con­ven­tional wa­ter heaters. For mod­er­ate-to-high users though, pay­back times will be rel­a­tively short.

Split sys­tems pric­ing ranges from $2,500 to $4500 de­pend­ing on size and brand. If the sys­tem can­not be plumbed into your ex­ist­ing hot wa­ter cylin­der (gen­er­ally those in­stalled be­fore 1988) you’ll need to ei­ther pay for a new one ($750 - $1500) or opt for an all-in-one sys­tem.

All-in-one sys­tems (which in­clude the tank) cost be­tween $2400 to $4500, plus in­stal­la­tion. All-in-one sys­tems must be ducted out­side to re­lease cold air and mois­ture.

In cal­cu­lat­ing the cost-ef­fec­tive­ness, pay­back and re­turn on in­vest­ment of these sys­tems com­pared to other wa­ter heat­ing op­tions, it is com­mon to take out the “sunk costs” of in­stalling or re­plac­ing a stan­dard hot wa­ter cylin­der, for ex­am­ple plumb­ing and elec­tri­cal labour. In the case of All-in-One sys­tems, this also means tak­ing out the cost of a stan­dard elec­tric el­e­ment cylin­der which is be­tween $1100-$2000. In these cases, the ex­tra (mar­ginal) 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.

Re­turn on in­vest­ment (ROI)

The ROI de­pends on the mar­ginal cost of the sys­tem, and the quan­tity of hot wa­ter be­ing used. In a new build en­vi­ron­ment, 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.

In a retrofit en­vi­ron­ment, 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 2 years.

The mar­ginal ROI for a fam­ily of four ren­o­vat­ing or build­ing a new home can range from 40-60% pa. When in­te­grated with So­lar Power (PV), a heat pump wa­ter heater can in­crease the ROI of the So­lar Power Sys­tem from 10 to 30% pa for a com­bined sys­tem.

Com­bined with a so­lar PV sys­tem, which pro­vides the elec­tri­cal en­ergy needed to heat your wa­ter dur­ing the day, sav­ings can be even greater.

Many com­pa­nies of­fer state­ments which de­scribe “sav­ings up to” how­ever what is con­sid­er­ably more re­al­is­tic are the com­pa­nies which guar­an­tee at least a min­i­mum level of per­for­mance. Ask for that guar­an­tee.

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