Beelbeebub

You open both and there should be a whoosh sound as water enters the system. You may need to turn the slotted screw on the right hand side (by the lever) so it is inline with the pipe. Wait until the pressure gets to the right level (usually about 1 bar) then shut bothaand return the screw to perpendicular to the pipe (as in the picture) . To be correct you should also undo the hose and store it away, but nobody ever does that A bigger question is why are you losing pressure. There are 2 possibilities. 1) the expansion vessel (the bug white cylinder) has failed. Every time the system warms up it over pressures and water leaks out of the pressure relief valve. 2) you have a leak somewhere in the system. Both will need looking at. Don't just keep topping up every few weeks. At best you'll rust out any radiators connected to the system. At worst you're dumping water somewhere in your house.

The point to note about output modulation is that it can be misleading to just think of a fixed % of the. Maximum. This is because the point at which you are likely to need the lowest output is usually when the outside temp is at it's highest Your HP mauly be able to modulate down to 25% of max output but that max output grows as the outside temp increaces So 25% of 5kw at - 5C is 1.25kw But if your output is 8kw at 15C it's 2kw. And your demand at 15C is lower than your demand at -5C. So for the true picture of modulation you need to look at your highest power output at the lowest OAT and your lowest power output at the highest OAT.

Thats a standard split aystem. The monoblocs are a single unit that fits in the room with no external unit at all, just 2 ducts to move air from outside, through the unit and then exhaust it. All you see on the outside are 2 air vents.

Wouldn't the high dT requirement not be an issue with a2a heating. The lower temp can be just above room temp ie about 20C or so. The biggest issue is the high pressure - over 100bar for the higher temps. I think this is at the upper limit of soft copper tubing

I looked at some monoblock a2a. Units where you just drill 2x.160mm holes in the wall. Powermatic make one plustthere are some Italian units (olympia splendid or something) The two big issues are prices - a couple of grand each and efficency. CoPs of about 3 tops. I can only guess this is down to the size limitations. Some US companies are looking at updated versions of the old window mounted AC systems. Unfortunately those are only really viable with sash windows which are standard in the US but not common over here except in period properties. They are ugly but do have the advantage of being very easy to fit. The best bet would be if we could get a refrigerant that has the low GWP of r290 (or similar) without the flammability issues. That way we could have DIY installs with precharged linesets using some sort of push fit connection. You just buy an outdoor unit, an indoor unit(s) and a premade lineset in an appropriate length from B&Q etc and away you go. If they could make air to water boxes that mimic the inside unit then you could provide DHW too.

Hi, Quick question. I have a WB Greenstar 30Ri supplying a thermal store and low temp (35Cish) Central heating system. I would like to move to an unvented cylinder for DHW and direct for the CH. Is there a way to have 2 set temps on the (WB) boiler depending on which system is calling for heat?

A occupational hazard listening to the world service 😁

The newer versions are interesting. They imply that if they go cold they simply stop working until they are reheated. Essentially go into hibernation. They also reframed the high (250-300c from memory) operating temp. Yes that's hot, but no hotter (cooler even) than temps encountered in an internal combustion engine. They use modern insulation materials to keep the heat in. But they also claim advantages to such high temps. Firstly, given all normal environmental temps are well below the operating temp the battery doesn't really notice the difference operating in 50C desert. Secondly the high temps mean dissapating the waste heat from internal resistance (charging and discharging) can be done with an emitter at 250-300c. Whereas a normal battery has to dissipate a few Kw at 40C. So the molten battery can use simple air cooling with a variable speed fan and a much smaller airflow. Whether or not anything comes of it, I thought it was an interesting alternative approach.

So. I had a gander and found this LA battery setup https://www.photonicuniverse.com/en/catalog/full/359-24kWh-48V-500Ah-AGM-deep-cycle-battery-bank-with-metal-racking-24-x-2V-batteries.html 24kwh, £2k Whilst a 9.5kwh Li pack is just over £3k. https://www.green2go.co.uk/givenergy-9-5kwh-lifepo4-unlimited-battery-integrated-dc-breaker-giv-bat9-5.html So game set and match for LA....right? 24kwh for 2k vs only 9.5kwh for £3k. Except the LA has a cycle life of 1200 cycles *at 30% DOD*. So it's really an 8kwh usable pack ie comparable to the Li pack and is only warranted for 1200 cycles/1 year, about 4 years daily use. The Li pack has an unlimited /12y warranty. So over the 12 years of the Li pack you will have had to buy 3 LA packs or £6k. LA's have had over a century to get cheaper and better. They are currently pretty much at their peak cost/performance point - plus they are made in vast volumes so there isn't much scope for reducing manufacturing costs. Li batteries and their cousins like Sodium ion are only at the start of thier development cycle. Volumes are still increasing, performance is still improving. I looked into solar PV 15 years ago when building my old house. And ran up against the battery issue. I couldnt find a way to make it work. So I went with solar thermal. Now it would be easy to sort out a battery PV system.

I don't think the life cycle costs of LA batteries is very good. They tend not to have very many cycles before needing to be replaced.

I think these are Sodium ion batteries rather than sodium sulphur. Basically the same tech as Lithium ion but with sodium (it's obviously more complex than that but that's the quick view). The big advantage being that sodium is very much cheaper and more availble than lithium. As a bonus the batteries are apparently longer lasting, less explosive and can withstand discharge to zero (making shipping much safer). There is a company looking at the molten sodium sulphur tech which has some interesting advantages or at least ways of thinking of the disadvantages (primarily the high temps needed) as advantages. IIRC these are extremely low energy density on volume and weight but have the advantage of being very cheap per kwh. For long term grid use the space/mass is not a problem.

Yes but if you have one oversized rad the DT will be larger, which means the DT of the other rads will need to be smaller. Assuming the lockshield etc are already at max your only option is to increace the flow through is to boost the pump head. Is that what happens?

I have been wondering, what is the effect of having an oversized radiator in your system. Say you have a perfectly set up system, the radiator in every room is the exact size required. The DT across each radiator is 5C. Now you swap one room for a gigantic raiditor, 3x bigger than needed. All else being equal, that room will be hotter if the DT across the rad is still 5C As you can't reduce the flow temp to reduce output because the other rooms will be too cold, your only option is to reduce the flow. But then the DT across that rad will be greater than 5C and that water will mix with the return from other rads so the DT the HP sees might be 7C. How does that work? Do we have to decrease the flow temp slightly and increace the flow rate so the DT. Across the other rads is smaller and the mixed DT is back to the 5C target?

Are there better ways of storing curtailment energy than as H2. H2 being produced from "waste"elec is not too bad for high value uses. But we still have other options for waste elec eg battery storage, cheap vehicle charging, thermal storage for domestic heating. We were speaking about hybrid Heatpumps being a misdirected bytgr FF industry to slow rollout of heat pumps. There may be some truth to that, but H2 domestic heat is the ultimate expression of that.

The absolute worst thing you could do with green hydrogen (if you had any spare) is pipecit into people's homes and burn it to keep them warm. Green H2 has it's place but that should only be for processes where it is absolutely irreplaceable chemically

You need the round trip efficency So elec >> H2 >> storage & transport >> heat

Really good

It does rather show how we are dragging our feet a bit. Counties that build out a significantly renewable grid will have a massive advantage going forward - just think what cheap power that isn't tied to geopolitical events would do for an economy and living standards.

If the UK added even at the rate that Pakistan added, despite being poorer, we would be approaching 100% renewable (aside from calm cloudy periods) grid by the end of the decade.

True, but there's against a backdrop of a total capacity of nearly 3,000Gw. So less than 10% Pakistan added 30%. By contrast the UK added...... 2.1Gw, about 3%

Grid scale baggery storage is getting cheaper and cheaper. And for the longer periods of low renewable there isn't a major problem with burning a bit of gas. We have the infrastructure already (existing Ccgt and gas storage) . Sure it releases some co2 but if we are only doing it for a few weeks a year who cares. The route is we just keep building out wind and solar. By the by, did any see that article about Pakistan adding 13Gw of solar, mainly in the form of small domestic and factory level units, in 2024, against a grid capacity of 46Gw!

Hydrogen is very much the fossil fuel industry "greenwashing" strategy. I doubt a single "Hydrogen ready" boiler will ever run on mains hydrogen. The logistical issues with simply blending H2 into the gas stream are too daunting let alone a full switch. I'm nearly as sceptical about H2 for grid scale storage. The round trip efficiencies are just too poor, especially given how difficult and dangerous H2 is to store in bulk. All hydrogen does is give cover for boiler maufactures and Gas suppliers to keep business as usual.

You make a point and badly done "fig leaf" hybrid installs probably won't help much. On the other hand, fear of spending more is a big issue for HPs. A cheap bolt on unit that effectively guarantees not to cost more than gas, has minimal disruption to the existing install. (eg no new cylinder, no massive replumb) has some potential. Clearly there will be some homes that cannot use a HP because the heat load is so large and/or the emitter are too small. But most homes in the UK aren't in that situation. Most people have upgraded the house with insulation, even if just loft insulation. Most people have double glazed windows. And crucially alot of radiators and pipe work was oversized for the 70C boiler flows. I've been encouraging some of my tenants to experiment by turning the flow temps down over the cold snap. One property, stone walled, steel framed window with some secondary glazing, semi with microbore pipes and P+ rads has been kept warm (OK as warm as before, 17C, the guy is trying to save money) with a 40C flow temp. Which surprised me alot. Another victorian ground floor corner flat with single glazed windows can hit 20C with 45C flows. That one has got some pretty big rads because it used to be famously cold so we chucked some massive k2 rads throughout. My point is both those places could probably manage with HPs and be cheaper. But they have combis (so hot water would cost a lot to fit and take up space) and I don't want to spend a bunch of money and the tenants complain it costs more to heat. If I could fit a box on the outside and a control box on thi inside for a grand or so after grant I think I would try that

In one sense that's a hybrid system, just with a slightly larger HP and a smaller (and cheaper to install) secondary heat source.

Grant seem to have a fair bit of experience with hybrid systems - you can (I think) still order an oil/HP hybrid unit from them but they also make some sort of advance interface box/buffer to link two separate units together.