Tue, 19 Dec 2023 06:26:36 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298219#Comment_298219 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298219#Comment_298219 Thu, 13 Oct 2022 03:11:47 +0100 omehegan
Now I'm thinking about the future, and what I would replace this boiler with when it's time to get off gas completely. It's just an academic question at the moment, but I am wondering what others would suggest. The house doesn't have ducts, and adding them would be complex, so any kind of ducted central system is probably out. Mini-splits in each room would be feasible and may be the way to go, ideally if I can control them from a central point. But the hydronic heat is nice for comfort, and I prefer it to fans and hot air blowing around the place. However my impression is that air to water heat pumps struggle to match the efficiency and performance of air to air ones for home heating. I suppose the other upside to air to air is that they can provide cooling in all rooms as well, something that we don't have today... I also note that there are more exotic things, like the Tepeo ZEB boiler. Maybe something like that will be a better option.

Thanks in advance for any thoughts!]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298221#Comment_298221 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298221#Comment_298221 Thu, 13 Oct 2022 09:06:42 +0100 Peter_in_Hungary
From what you say to me it sounds like air to air with mini-splits doing both heating and cooling would be the way to go.

On the other hand

Any opportunity for lots of your own PV? Over here our PV is reconciled annually so summer over production can be used in the winter. This means that an electric combi boiler could be used at zero running cost if your annual PV output was enough to support your winter heat load. If you could do something similar then an electric combi would be a 'plug and play' option for your existing system and much cheaper than other options although the cost of the PV would need to be factored in - but then are you having PV anyway and this just means more of it.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298242#Comment_298242 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298242#Comment_298242 Fri, 14 Oct 2022 03:12:21 +0100 omehegan
I am definitely planning to add PV as soon as I can, but I'm not sure how much I'll be able to put in. Hipped roof on the house with two ridges facing north, and then a garage I can use, but with a tree in between garage and house that will shade some panels at different times of the day. I'm not sure I could fit more than about 6 kW north-facing. Also our PV generation isn't reconciled in the way you describe - we just get a flat feed-in tariff all year round, and that is slowly shrinking as the deployment of solar increases.

Now that I think about it, a central air-to-air heat pump could be feasible, but the ducting would have to all be in the attic with vents into the ceilings - the house has no crawl space, so ducts and vents under the floor are not possible.

It would just be a bit of a shame to have to remove the whole hydronic system just because there isn't an electric heat solution that suits it. But maybe that is just the future reality...]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298243#Comment_298243 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298243#Comment_298243 Fri, 14 Oct 2022 06:10:43 +0100 tony http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298244#Comment_298244 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298244#Comment_298244 Fri, 14 Oct 2022 09:32:13 +0100 WillInAberdeen
I had heard that the biggest heat pump market in the world is for air-to-air heatpumps (aka aircon). But that there is a much smaller market for air-to-water, for those Northern countries that are heavily invested in water-based central heating and don't use air conditioning. So prices and availability of air-to-water are not yet as good as air-to-air. But is that true? What's it like in Melbourne?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298245#Comment_298245 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298245#Comment_298245 Fri, 14 Oct 2022 09:40:37 +0100 Peter_in_Hungary
With air to air HP DHW needs resolving.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298247#Comment_298247 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298247#Comment_298247 Fri, 14 Oct 2022 10:31:04 +0100 WillInAberdeen
1) the new generation of R32 ashps now have high efficiency at the same highish flow temperatures (~60⁰) as a condensing boiler, they have been designed to be drop-in boiler replacements.

2) the optional cost to replace our radiators was a relatively small component (10-20%) of the total cost of the heat pump.

3) edit: and same as Peter, many of our existing radiators were already oversized, either because insulation has reduced loads, or because original boiler installer had bumped up the radiator sizes due to vague wet-finger sizing methods.


In the end we didn't go ahead because the local installers here were swamped with demand and so had given up on customer service. Waiting to see if the installer market here catches up with demand.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298248#Comment_298248 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298248#Comment_298248 Fri, 14 Oct 2022 12:58:54 +0100 djh Posted By: WillInAberdeenI had heard that the biggest heat pump market in the world is for air-to-air heatpumps (aka aircon). But that there is a much smaller market for air-to-water, for those Northern countries that are heavily invested in water-based central heating and don't use air conditioning. So prices and availability of air-to-water are not yet as good as air-to-air. But is that true?I believe so. Most private houses and apartments in warm countries with any disposable income have multiple air-conditioning units, or multi-splits. Pretty much every international hotel chain room, and even national or local hotels in warm countries, has aircon. A lot of cars have aircon. Many schools and offices have aircon etc etc. Fridges and freezers are air-to-air heat pumps.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298266#Comment_298266 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298266#Comment_298266 Mon, 17 Oct 2022 02:04:44 +0100 omehegan
You CAN get air-to-water heat pumps here, for example these are sold by the company that installed my gas boiler: https://www.hydronic.com.au/products/heat-pump/ But the boiler they installed is a 30 Kw unit, whereas these HPs are 14-16 Kw maximum. That would seem to suggest that I would need two of them to handle the heating load, and that's consistent with what I have read anecdotally from people who have installed them. Just one of these 14 Kw units sells for around $18k AUD, compared to just under $10k AUD that I paid for the gas boiler. And compared to around $6k AUD to purchase 4x mini split units I would need to just switch over to air-to-air units. At these prices, it's hard to see why anyone would install an air-to-water system. I could still easily afford to switch to a stand-alone heat pump hot water heater at those prices.

Today, Melbourne doesn't have too many really hot days in the year, and so our solid brick house hard up against the houses on either side doesn't tend to heat up that much in the summer. It takes a string of 3+ hot days before it starts to get uncomfortable inside. That's how we are able to make do without AC in any of the bedrooms. But if we assume that average temperatures are only going to get hotter over my lifetime, then both price and flexibility (heat and cool) seem to suggest that the mini-splits will be the way to go.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298268#Comment_298268 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298268#Comment_298268 Mon, 17 Oct 2022 09:30:13 +0100 WillInAberdeen
The 30kW combi boiler rating is normally because it provides a lot of instantaneous hot water, it doesn't need anything like that many kW to heat the house. In our climate, a 16kW heatpump would be plenty for a large detached Victorian-era house, and 12kW is a normal size for anything smaller or better insulated. Then you add a hot water tank that it can heat up more slowly (although 12kW can reheat plenty quickly after a shower).


I would go with something that is 'normal' where you are, with a large pool of installers and service people. You don't want to install something niche as the specialist installers are expensive and you won't get it fixed easily if it breaks down the line. If aircon in houses is not unusual where you are, then likely there will be plenty of service companies.

The market is changing quite quickly here, so perhaps by the time you are ready to replace the gas boiler it will look different. You can cover your bases by insulating the house, that won't be wasted effort, irrespective what system you end up with. Pick out likely locations for the outdoor units and their cable/pipe runs, and try to avoid obstructing them as you improve the house.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298301#Comment_298301 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298301#Comment_298301 Wed, 19 Oct 2022 03:33:16 +0100 omehegan
So, maybe in theory I could get away with just one heat pump boiler of around 16 Kw. Today that would still cost 3x the price of the 4 additional mini-splits I could use instead. Also, if I understand right, the heat pump boiler requires a buffer water tank that may have to be indoors. I doubt I could find space for something like that - my regular water heater is outdoors.

But you're right, time will tell as the market shifts over the next few years.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298303#Comment_298303 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17603&Focus=298303#Comment_298303 Wed, 19 Oct 2022 11:24:18 +0100 djh