ProDave

My only "concern" at the moment about putting together your own control system, is setting the temperature set point of heat pump. The only control interconnection to the heat pump was a 2 core cable between the controller and the heat pump. So it must be using some form of serial interface. Why do I get the feeling that finding the information on what that interface is, and the communication structure is going to be difficult, and even harder to find out before you buy a heat pump At the end of the day, all I want to be able to do is turn the heat pump on and off, and select it's heat output temperature. a requirement that should not be difficult, but with a system sold to be used with a packaged control system that might not be so easy to find out.

I thought your question about the store had been answered. Yes if using a tank like this one that uses a plate heat exchanger, then you need a circulating pump. I would much prefer a cylinder like the one Jack has, with a large area heat input coil. No need for a dedicated pump or the controls that go with it. I also share your concerns about servicability of this system. The control board looked every bit as complicated as a PC mother board, and it's a proprietary item not an off the shelf mother board. So if it goes wrong I just know that's going to be a lot of £££ for a replacement, and in 10 or 20 years will you even be able to buy a replacement? That is why I am so keen to put together a system with simple passive pats and standard central heating control parts. Where that's not possible, any missing control parts will be designed by me and if they go wrong I can fix them, or design a replacement if technology has moved on. That's the theory anyway. I am currently thinking of using an arduino or a Pi as the controller.

I suspect the "heat exchange coil too small" was just the installer pushing this cylinder with a plate heat exchanger. Personally like you I would prefer s simple cylinder with a large area heat input coil as it makes a very much simpler system, and almost certainly one that's easier to put together as a system yourself. I am not sold on this weather compensation stuff. I would try and turn that off, or set the curve flat. The house heating controls should take care of putting more heat in when it's colder.

I didn't see the installer do any "programming" Yes I saw an SD card slot on the board under that square cover on the cyilider but didn't see anything plugged into it, and I never saw him carying a pc with him. All I saw him do is go through some menu's on the programmer that came with it and set up some parameters. I suspect the SD card is used for software updates and they think putting that in the sales blurb makes it look sophisticated. Sory to me it just makes it lok over complicated.

Do some research. Start by reading this http://forums.moneysavingexpert.com/showthread.php?t=4399311&page=8#topofpage Hotel California, You can switch supplier but you can never leave.

Terry, I think the thermostat issue is one with mechanical thermostats. Fit one with an electronic sensor and it should have much lower hysteresis. Also the situation you describe would only happen if the water flow temperature was too high and it put too much heat into the slab in one go. As with any control system, it will need some tuning to prevent overshoot. It's just that it takes a long time to tune such a system.

I must have the same vents (bought them from ebay) and they came with the same triangle bits that I have not used. So I too am interested to know what I should have done with them.

You mentioned a boiler flue. THAT would concern me more, achieving a proper separation between that and the mvhr vents. What does building regs say about that?

That is a VERY interesting price list. To buy this 8KW mitsubishi air source heat pump and the pre plumbed cylinder would cost £3715 from that price list (presumably plus VAT which on a new build you would get back.) I know for a fact, in this case, the owner has paid in the region of £16K for a local renewable heating contractor to install it. Some of this he will get back via the Renewable Heat Initiative (I will attempt to find out how much) It has so far taken 3 man days to install it, one man yesterday, and two today. I believe he is coming back again tomorrow to plumb in the solar thermal bit, so lets say 4 man days total to install. So lets work on a Plumber in the Highlands charging about £200 per man day, that should be about £800 in installation costs. bringing the total to about £4515. Lets say £5000 total to allow for some pipe and fittings and to make the sums simple. No lets round that up to £6K in case I have under estimated just how much a plumber charges. So (me being very cynical) thinks they are charging something like a £10K "RHI premium" to install this system. So the big question has to be, will you get £10K back in RHI payments? If the answer is no, then I would personally say, avoid getting a packaged, installed system at RHI prices. This confirms my rather cyincal view, that the only people that benefit from the RHI scheme, is the installers who can bump up their prices and charge a premium. This also confirms the view of a poster on ebuild who had concluded much the same thing that it was a lot cheaper to self install and forget the RHI altogether. When the time comes for my own system, I am tempted to get the same renewables company to quote, then look up the component prices and an estimate of reasonable installation costs, and ask them to justify their premium price.

My understanding is this is an unvented water tank, so cold mains water (via PRV) goes in at the bottom and hot water to the hot taps comes out of the top. You would normally heat this type of tank with a heat exchange coil at the bottom. But because you are heating it with low temperature water from the HP, it would need a particularly large heat exchange coil. So instead it is heated by a plate heat exchanger. So the water / antifreeze / inhibitor mix of the closed circuit heating circuit passes through one side of the plate heat exchanger, and water from the tank is pumped through the other side via two tappings to the tank. So it only needs power and a pump running while the cylinder is being heated. Once hot, you can draw hot water from it in the same way as any other unvented cylinder without any power. There are 3 pumps on this tank. One is to circulate the hot water via the PHE. One is to circulate the heating circuit to the ASHP whenever that is running, and the third is to circulate heating water to the heating circuit, in this case UFH. I did like this system for what it does and how it does it. but my feeling is the "controls" side of it lack integration. There is a very complicated controller, which I strongly suspect is beyond the ability of most normal home owners to understand or adjust. Then in this case there is a completely separate under floor heating controller with it's own timer clock etc. There is almost no integration between the two. That is probably the fault of the home owner who in this case had originally planned to heat the house with an oil boiler, until he found that it was not possible to get a SAP "pass" with just an oil boiler so he rather reluctantly I think chose the ASHP system. I am still minded to put my own system together along these lines, but built from individual components with a simpler and perhaps better integrated control solution.

Almost. It is actually this cylinder https://heating.mitsubishielectric.co.uk/Products/Pages/Monobloc_Pre-Plumbed_Slimline_Cylinders.aspx And I believe it's an 8KW monoblock heat pump/

Yes, but in a really well insulated house, you would not set the UFH temperature to 10 degrees above room temp, you would set it lower. I think the main point is no need to go via a buffer tank between the ASHP and UFH, and no need to heat the water any hotter than the target floor temperature (so the heat pump can run at a lower temoperature and hopefully better COP. One think I did notice, which I will probably be asked to correct later, is the installer did not use the "call for heat" from the UFH controller. So at the moment it looks like the ASHP would still be left idling heating just a short loop if the UFH was satisfied. So in any event the UFH controller with it's room stats would stop the house cooking. In case it's not clear, the system I am describing is not in my own house, but the new build I have just about finished wiring today.

Yes. Just bear in mind, if you are wanting to position the sensor on the ceiling to line up with something else, that the cable entry into an Aico sensor is NOT in the middle, but close to the edge. So if exact position is important, the cable needs to come out of the ceiling about 5cm out from where the centre of the sensor will be.

I was working today on a new build that was having the "professionally" designed and installed heating system commissioned,so I took some time to have a look and talk to the guys. It was a Mitsubishi ASHP coupled to a "pre plumbed" Mitsubishi cylinder and controls. The nuggets of information I gleaned, in no particular order were: The tank was an unvented cylinder for hot water only. Heated to 45 degrees by the heat pump. Once every 3 weeks, on a day of the week of your choosing, it automatically uses the immersion heater to raise the tank to 60 degrees for an hour as an anti legionella measure. Because of the low grade heat input, they said it would require too large a heat input coil, so it used a plate heat exchanger to heat the tank. The UFH runs directly from the heat pump. No buffer tank. It either runs DHW or heating, never both together. When in heating mode, the heat pump runs at a low temperature which you can set. They say this obviates the need for UFH mainifolds with temperature control, instead you can use a dumb manifold (cheaper) and just dial up the flow temperature you want for the UFH in the heat pump controller. The outside unit ran very quietly, and I didn't see it icing up or needing to defrost, it was about 3 degrees today. I was particularly interested in the no buffer tank, and direct operation of the UFH with a dumb manifold. Certainly something to think about.

You can comfortably get two cables into an aico terminal box. If you are really tidy, and use 1mm (not 1.5) you can get 3 in if you want to make a spur.

Okay, I will ask a dumb question. What is the purpose of an overflow? I can only assume it's for if you put the plug in, tirn on the tap, then go away and forgert you have left the tap running. I don't think I can recall ever having a situation where the overflow overflowed. I could live without one.

Is that training for you or her? (I think we know the answer)

Why can't it go through the wall of the plant room, i.e at ground floor level? Why does it have to go up through the joists to exit at first floor level?

I hope that is wired as a 2 way switching system, otherwise you (or SWMBO) will get very annoyed at having to go upstairs to turn on the "downstairs master switch" As a point of principle I almost always wire the hall switch as 2 way switching upstairs and down as well as the landing light (how any times have you gone upstairs to bed and realised the hall light is still on)

I cold have done, if I had known of this requirement, I could have ran a stack up the gable end of the garage. But by the time I kenw about it, that was already concreted over as a parking space, so we will live with the stack through the roof now.

You can well argue that a garage is permanent. I argued I had no intention of removing the static caravan, but BC would not accept that, saying any future owner of the house may remove it and cap the drain leaving it with no vent.

I think your BBC link is wrong. It seems to take me to an advert for a bathroom suite.

Can you post the EXACT title or the article. Makes it easier to google

I agree with that. I wanted to avoid a vent through the roof. The end of my run is actually the static caravan which has a vented stack, so I argued that I only needed an AAV in the house. But BC would not accept that saying there must be at least one vent from the house. That house vent could be just a stack running up the outside of the house, but I think that would have looked awful, so I went for a vent through the roof.

But will a bin lorry go down a private road? They don't here. In such a situation, everyone wheels their bin to where the private road joins the public road and they get emptied from there, or not at all.