@jancold I changed things a bit with 🐙 by insisting rooms had other functions - spare bedroom = office. 
I've accepted their install won't be perfect (as in for my needs) but they are so much cheaper it is all I can afford.
Hopefully, over time, it is tweakable one way or another. 

Posted by: @lucia

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@jancold I changed things a bit with 🐙 by insisting rooms had other functions - spare bedroom = office. 
I've accepted their install won't be perfect (as in for my needs) but they are so much cheaper it is all I can afford.
Hopefully, over time, it is tweakable one way or another. 

@Ian McKay Assuming you don’t require dynamic temperature changes and are happy with a constant temperature in any one room, please carry out the control of temperature using the lock shield valve at the opposite end of the radiator from the TRV (which should be fully open, then the lock shield valve will control the flow.) If you wish to follow my routine, please read:

https://renewableheatinghub.co.uk/how-to-balance-radiators-the-role-of-the-lockshield-valve

Regards, Toodles.

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Interesting thoughts Simon. One thing that troubles me about the recommendation to avoid using TRVs is that the user then has little control over individual room temperatures. How would you suggest the occupant makes those kinds of fine tuning adjustments?

As @toodles says above.  Basically you don't except as a one off when the system is commissioned (or over time) by balancing the radiators using the lockshield valves.

Low temperature heating, whether by gas, oil, or heat pump, is a different design and control philosophy to the high temperature heating we are used to.  The basic idea is to dispense with most controls and run the 'boiler' (gas, oil or heat pump) more or less constantly at the lowest possible temperature so that the heat loss from the house is just matched by the heat emitted from the radiators.  This gives both the maximum efficiency and the maximum comfort (the latter principally because temperature gradients are minimised).  The efficiency gain is more with heat pumps than with fossil fuel boilers, which is why it is emphasised in heat pump installations, but is present even with fossil fuel boilers.  The supposed gains from micro-controls, much touted by the manufacturers, are largely wholly illusory and certainly well over stated. 

You may need to read a bit more fully to understand this as there are a few interacting factors some of which are counter intuitive.  It boils down to keeping most emitters open all of the time gives you a nice constant temperature with minimal temperature gradients in the room (hence maximum comfort) for the least expenditure of energy.  The reason that this is the most efficient boils down to the fact that the heat loss from the house is determined by the insulation between the house and the outside walls and insulation between rooms is negligible.  The upshot of this is that the amount of heat loss (from the house) saved by zoning a room or an area is quite small, and the reduction is more than offset (in many cases) by the loss in efficiency due to the reduced emitter area which means that the flow temperature must be increased to compensate, resulting in a higher energy consumption (which is what you pay for) even though the loss from the house is less. Heat Geek has some good videos on why not to zone (and when zoning might be a good idea), with some worked examples to prove the point.

Most of us should really be running our gas boilers this way too, but unfortunately the UK (unlike some other countries) didn't mandate weather compensation, so it wasn't applied even though most boilers support it because the industry in Europe is centred on Germany which does mandate it.  As a consequence most of us are probably paying 10% more for our heating than we need to and have been suckered by the control industry into buying way more 'bits' than we really need to.

Hi I am thinking of having a heat pump fitted the installation company is MPC Titan Business Park 1 Aurora Avenue Queens Quay Glasgow.
I currently have oil-fired heating and is a 25 KWH the house is a 3-bed detached bungalow with a solid 9-inch thick wall what size pump would be required and can they use the existing pie work for the radiators they will replace the radiators
I consume 1800 liters per year

1 do you have any experience with MPC
2 would it be cheaper to run a heat pump
3 the house is a constant 20c
any advice would be appreciated thank you, Ian.

@Ian Cruickshank

We would need some more details to answers all your questions on heat pump size and pipe diameters, but it is possible to give you a rough idea from the 1800 litres of oil per year. There are various methods that can be used but as a rough guide I would estimate that you would require a heat pump with a maximum output of between 6-8 kW.

If you have 15mm copper pipes to your radiators then thats a good first indicator.

An installer would do a full heat loss survey, which might be higher (they frequently are) but be wary about going too large. bigger is not always better in heat pumps.

With respect to running costs, a well installed heat pump should beat oil and gas, but well installed are the key words. there are a lot of installers out there who just harvest the grant without really knowing what they are doing. I would try and get quotes from heat geek installers as a first option.

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Hi I am thinking of having a heat pump fitted the installation company is MPC Titan Business Park 1 Aurora Avenue Queens Quay Glasgow.
I currently have oil-fired heating and is a 25 KWH the house is a 3-bed detached bungalow with a solid 9-inch thick wall what size pump would be required and can they use the existing pie work for the radiators they will replace the radiators
I consume 1800 liters per year

1 do you have any experience with MPC
2 would it be cheaper to run a heat pump
3 the house is a constant 20c
any advice would be appreciated thank you, Ian.

On the basis that oil is 10kWh per litre, 1800 litres is about 18MWh.  That very roughly translates to a 7-9kW heat pump.  You will need to have a proper heat loss calculation done to size the pump, but if it differs widely from this then question it.  You may need to replace some or all radiators depending on their sizes, heat loss calc will indicate.  You should get a scop of 3 or better so will consume 6MWh electricity per year or maybe less.  You can work out how much that costs.  

Heat pumps are all about the system design not the unit itself.  Many installers simply dont understand how to design a low temperature heating system and will add in lots of unnecessary controls, a buffer tank and miscellaneous other things which cost money and compromise performance.  Simple is best, no buffer, one zone, no TRVs on the majority of rads (or TRVs turned up to 2-3 degrees above the target temperature).  No third party 'smart ' controls (with one possible exception - homely), just weather compensation driven by the heat pumps own controller.  Diverter valve so either DHW or CH is fed never both at once.  Initially run 24*7 for most of the season with possibly a modest set back at night.  You can vary this either end of the season.

Its worth following this forum to understand the technology better, sadly many installation companies, set up especially to harvest the grant, don't. 

I know nothing about MPC.

Hope that helps.

PS.  I should have added that the heat pump capacity you need may be up to 25% less if you have a very old (ie inefficient) boiler.  In the range 6-9kW is probably a good assumption (subject to survey), anyone trying to sell you say 10+ KW is, as @bontwoody says, suspect.  One cowbow lot tried to sell me 2*16kW pumps for my 8kW house!
Be aware, however, that heat pump sticker capacities arent necessarily representative of their actual capacity and the actual capacity depends on the design temperature.  Vaillant, for example, sell a sticker 7kW model which, in the South of England, is good for 8.5kW.  Mitsubishi and Samsung seem to clamp their output at the sticker value in firmware, as it is suspiciously constant over a range of outdoor temperatures.  Daikin, who sell half a dozen models in any given 'range' seem to do fairly weird things.  Other manufacturers have other variants.  This is part o0f the selection process that your designer will go through.

Please keep us posted with any progress and if there is anything you are unsure about, there are numerous very knowledgable and helpful people who subscribe to this hub - and advice is unbiased and free! Remember, there is no such thing as a silly question - personally, I have gained a great deal of understanding from subscribers questions and the replies on this group! Regards, Toodles (I’m just here for the free ride m’self😉)

First posting.
I have had an ASHP since 2009 and sometimes I think I know less now than I did then.
I read and appreciated the article on the 6 flags. It did prompt a couple of questions.
I think questions first and then a bit of info to help if someone wants to try and explain to me.
Red Flag 1: Design Flow Temperature.
If the system is set to produce 35’C. How do you get water sufficiently hot for DHW?
I have found from experience that 45’C at the tank is fine for showers, but 40’C and it might start to run cool at the shower by the end. ASHP cannot keep up with demand?

Red Flag 4: Buffers, Hydronic Separation & Fixed Speed Circulation Pumps.
This is the big question.
Is the buffer that is referred to, the same as my cylinder? Or did I misunderstand?
All the ASHP systems that I see advertised have an external fan unit plus an internal cylinder.  

Background info. Probably too much?
2009 a 4.5kW Sanyo monobloc system installed.
223 litre cylinder. The DHW coil running through it is 5 litre capacity. The ASHP dumps into that tank. The CH radiators run from the same tank.
The pump for the external ASHP fan unit is Fixed speed. The pump for the CH radiator system is set on a low fixed speed, just because that seems to work.
A small 3-bedroom Victorian terrace in London. Now, well insulated. For example all windows and external doors either DG or TG. 100mm PIR internal insulation on some external bedroom walls. 150mm PIR insulation at Loft floor level. Started to insulate at ground floor level, 100mm PIR between joists. Still insulation work to be done.
Radiators all upgraded. (No radiators in two bedrooms. Those are being renovated and have the benefit of IWI (internal wall insulation).

Impossible to state exactly the ASHP electric consumption but from the detailed meter readings that I take, I would work it out at about 10kW per day, for a Feb 2024 period in inner London.
Occupancy – 1 person.
I leave the ASHP as ON 24/7. The heating is programmed for morning and evening periods. Manually boosted if I get chilly outside of those periods.

Unfortunately, I don’t know my Heat Loss calc. Nor do I know the Heat/Temp Curve for the Sanyo. The user interface is horrible.

I want to learn because the unit is not going to last for ever. One day I must make a big decision.

Right now I am NOT looking for recommendations, just guidance on the two points above. 

@gt22 Welcome to the forums! Here are my thoughts on your questions:

Red Flag 1: Design Flow Temperature – When your system runs at a 35°C flow temperature for space heating, domestic hot water (DHW) is generally handled separately. Modern systems are designed to use different flow temperatures for heating and hot water. The heat pump will typically boost its output to around 50–55°C specifically for DHW, so they don’t interfere with each other.

Red Flag 4: Buffers, Hydronic Separation & Fixed Speed Circulation Pumps – The buffer tank being referred to here is separate from your hot water cylinder. In the heating circuit, the buffer tank helps “smooth out” the ASHP’s operation and reduces short cycling, particularly with fixed-speed pumps. Your hot water cylinder is dedicated solely to DHW and doesn’t interact directly with the buffer.

If you’re open to it, sharing a photo of your plant room where the hot water cylinder is located could help determine if you’ve got a buffer tank in place.

You’ve really been a trailblazer with your 2009 ASHP! Ours is only six years old, and the control panel already feels outdated, so I can imagine the quirks of your Sanyo. Would love to see a photo of the unit if you’re willing to share.

Posted by: @gt22

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2009 a 4.5kW Sanyo monobloc system installed.
223 litre cylinder. The DHW coil running through it is 5 litre capacity. The ASHP dumps into that tank. The CH radiators run from the same tank.

So you have a very different system. You have a thermal store, so the heat pump only produces a single flow temperature. Based on being 2009 install you may have a non-inverter heat pump. So the install is quite different. In your install the buffer and hot water cylinder are sort of the same thing.

Typically a new heat pump runs CH and DHW at different temperatures. This gives a gain in CoP (but only if the CH is designed for low temperature).

So the red flags do not really apply to your install.

I would not be that concerned about your install, as the heat pump design is done around a reasonable flow temperature, you will get decent run times and a good delta T, so this improves things quite a bit.