Pre-heating water for instant gas or electricity boiler

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Disrespective

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#1401111 6-Oct-2015 16:16

Is it cost efficiency you are after?

If so, the Steibel Eltron underbench instant hot water systems aren't necessarily any better or worse than others, but are good in other areas.

MikeAqua

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#1401122 6-Oct-2015 16:16

For a one person dwelling solar pre-heating is going to be a big outlay. I would get either a gas califont or electric HWC and be done with it. Maybe solar PV top assiste with an electric HWC. SA the primary use of HW is in the morning it has all day to use solar PV to power a reheat.

Regarding the house design: Passive solar heating only in Well ... what happens if it's cold and wet for three days? There is no such thing as prefect insulation. The laws of thermodynamics say you will lose heat, and if the sun isn't shining ...

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gchiu

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#1401246 6-Oct-2015 19:31

Appliances such as TVs, X-Box, dish washers, refridgerators etc all generate heat, and these are employed in the passivhaus design to maintain internal house temperatures.

But I have a backup plan to stick a couple of far infrared panels on the ceilings if his calculations are off!

bfginger

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#1401949 7-Oct-2015 18:33

Gas cooktops are good but gas ovens have a bad reputation and there are very few on the market in New Zealand so choose carefully.

Outdoors rated hot water cylinders are usually very well insulated. If high wattage is a problem you could ask for a smaller than normal element in the cylinder.

http://www.rheem.co.nz/hot-water-cylinders/

Solar hot water equipment isn't expensive but there has been huge overcharging by installers that has given it that reputation.

I would be sceptical of claims a house doesn't need heating. The walls may be heavily insulated but if it has standard low quality New Zealand windows it will lose most of the heat through them. Even if it doesn't need heating a heat pump may be useful to cool the place in summer.

You could get a small wall unit for ventilation. Opening windows isn't a very effective method.

http://simx.co.nz/SmartVent-Synergy.php

gchiu

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#1401991 7-Oct-2015 20:09

I've seen the price of solar hot water on Aliexpress, and it's not expensive at all. But then add in transport to NZ, and installation ... it then becomes uneconomic.

I think heating/ventilation can be added later on if it turns out it's needed. But she's got full height sliding glass doors across one whole side of the house, and small ceiling windows on the opposite side so that should allow plenty of ventilation. The glass will all be thermally broken double glazed. and again we can add in thermal curtains if it's not enough.

I did investigate the Smarvent a year ago but they told me it's only suitable for a bathroom sized room.

Good idea on the smaller then normal element for the cylinder. I'll make enquiries.

Aredwood

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#1402069 7-Oct-2015 23:00

Just get a large capacity electric hot water cylinder and heat it via night rate power with Flick electric. Get one of the Rheem stainless steel cylinders. http://www.rheem.co.nz/stainless-steel-mains-pressure-water-heaters/product/32530005-0A/ As this cylinder has 2 element ports. As well as connections for solar thermal or heatpump. If you want to add solar PV, Simply move the mains element to the top port. And install a solar element to the bottom port. But for now since you have said it will be just 1 person using it. You are unlikely to save enough on running costs to recoup anything spent on heatpump or solar water heating. But if usage goes up and you want to add solar or heatpump later. The above cylinder can be reused.

As for gas - is the pipe still sticking out of the ground where the meter used to be? If so contact the gas network company in your area. (think it is Powerco in the Wellington region) And ask about a "meter rehang". They used to be doing a promotion where they will reinstall a meter for free. (maybe they still are) But of course you have to then start using gas or at least paying the normal fixed fees. If it will be a very long pipe run from the meter to the house. Ask for a 7KpA regulator to be installed on the meter. So you can use a smaller pipe due to the higher pressure. But you then need a stepdown regulator at the house end.

And for the peak loading. Definitely get a gas hob. And run off a 9Kg bottle if no other gas appliances. And you could always connect the hot water cylinder and the oven to a changeover switch. So only one will draw power at a time. As long as the daughter remembers to switch the oven off at the wall when finished cooking. (so the hot water cylinder can reheat).

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#1402149 8-Oct-2015 09:11

If you can get electricity at 8c/kw overnight, and she showers in the morning then I would say just go with the standard cylinder.

Its not worth spending any more money on it at that rate.

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MikeAqua

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#1402359 8-Oct-2015 13:02

Even inert filled e-glass DG has a pretty poor R value. Triple glazing is better but the price is

I would be sceptical of claims a house doesn't need heating. The walls may be heavily insulated but if it has standard low quality New Zealand windows it will lose most of the heat through them. Even if it doesn't need heating a heat pump may be useful to cool the place in summer.

Mike

MikeAqua

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#1402366 8-Oct-2015 13:14

Sure, and people, cats and dogs generate heat too.

But heat is lost to doors/windows extraction fans etc.

For example ...

Our (modern) house in Nelson has R3 or higher batts everywhere, plus polyblock walls, high end DG and thermal drapes ...

On a cold day with 2 cats, 1 dog and four adult sized humans all watching movies we still need to use the heat pump.

And I'm talking Nelson cold not Welly cold.

Disclaimer: I can't say with full confidence that the pets were actually watching the movies but they were in the room.

gchiu: Appliances such as TVs, X-Box, dish washers, refridgerators etc all generate heat, and these are employed in the passivhaus design to maintain internal house temperatures.

But I have a backup plan to stick a couple of far infrared panels on the ceilings if his calculations are off!

Mike

gchiu

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#1402424 8-Oct-2015 14:00

https://en.wikipedia.org/wiki/Passive_house

"In addition to using passive solar gain, Passivhaus buildings make extensive use of their intrinsic heat from internal sources—such as waste heat from lighting, white goods (major appliances) and other electrical devices (but not dedicated heaters)—as well as body heat from the people and other animals inside the building. This is due to the fact that people, on average, emit heat equivalent to 100 watts each of radiated thermal energy.

Together with the comprehensive energy conservation measures taken, this means that a conventional central heating system is not necessary, although they are sometimes installed due to client skepticism.[42]

Instead, Passive houses sometimes have a dual purpose 800 to 1,500 watt heating and/or cooling element integrated with the supply air duct of the ventilation system, for use during the coldest days. It is fundamental to the design that all the heat required can be transported by the normal low air volume required for ventilation. A maximum air temperature of 50 °C (122 °F) is applied, to prevent any possible smell of scorching from dust that escapes the filters in the system."

Now we're not in Europe, and we don't normally get to such low temperatures as to get snow in Wellington, so she may be okay with superinsulation as per passivhaus design. But if not, adding a few heaters as a retrofit is not going to be difficult. That would be preferable to the cost of German triple glazed windows.

gchiu

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#2189071 28-Feb-2019 20:30

It's taken 3.5 years to get this 45 m2 house built! The final council inspection was last week, and the cost was over 200% over budget :(

She's got two 45 kg gas cylinders to heat the hot water using a califont. On the sunless days we had last week the house did get a bit cold but she didn't need to borrow a heater. But I suspect it will get colder.

The 8c flick night rate disappeared ages ago so we're glad we did not go for a large electric HWC.

I guess I'm back to thinking about a DIY solar preheat again.

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#2189174 1-Mar-2019 03:31

Alot has definitely changed since I wrote my previous post in this thread. Sure, no more cheap night rate power (I miss those nights of cheap power with Flick).

But we now have the wildcard of the oil drilling ban. If the claims are true, then we will run out of gas in 7 to 10 years time.

And another wildcard, will the low user regulations be repealed? If so then per unit rates will become alot cheaper. And fixed rates alot more expensive. Especially if the government starts investigating why it is cheaper for end consumers. To pay for fossil fuels to be delivered to their houses using trucks that also burn fossil fuels. Instead of using the electricity that is already delivered to their house. And which is approx 80% from renewable sources.

Either could cause the large cylinder to become more economical again.

gchiu

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#2189248 1-Mar-2019 09:54

I very much doubt that our gas reserves will become depleted. If the current reserves look to reach such a point, the realists will reinstitute drilling, or a National govt will have returned to power and drop the ban. There are too many households dependent on gas for cooking and heating. But if it ever did become uneconomic I guess I would go for a solar preheat, and the final heat with an electric on demand heater rather than have a large cylinder.

To ever use natural gas again they need to drop their high line charges. I suspect that's a major reason why people move to LPG. They should factor in the line charge in the unit charge.

gchiu

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#2189332 1-Mar-2019 12:15

Disrespective: Is it cost efficiency you are after?

If so, the Steibel Eltron underbench instant hot water systems aren't necessarily any better or worse than others, but are good in other areas.

The Steibel Eltron instant hot water devices can't do a shower. The DHCE is limited to 6 lpm whereas an energy efficient shower head uses 8-9 lpm.

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