I'm not sure they necessarily remove the need for a buffer tank. The advantage seems to be that there is no need for refrigerant piping and therefore an easier and cheaper install, as well as can be installed by someone who isn't F-gas qualified.
I am interested. We have a fairly new oil boiler but its the last fossil fuel we use (aside from 10l a year in the lawn mower). I'm not convinced the cost/benefit is there yet. I think were i to go for it I would indeed have a big buffer tank somewhere so I could run the heat pump flat out for 6 hours in Intelligent Octopus and hope my 15kWh battery storage covered most of the top up demand through the day (we already run the batteries flat in the depths of winter)

 

Thanks for that, reading up I agree I was mistaken and a buffer is still recommended, although as you say the installation is still simpler so i still find it ofd it wasn’t mentioned

looking around one option if space is an issue is a HWT with a buffer tank inside

 

Monobloc or split system, a heat pump won't work with conventional radiators as the circulating temperatures are much lower than a fossil boiler.
Split systems have the advantage that the outside pipework carries refrigerant, with the heat exchanger being indoors, helping efficiency. The disadvantage is a higher likelihood of refrigerant leak, with more connections in the system.
A buffer tank is needed in most radiator systems, but can sometimes be omitted with underfloor heating.
Sadly, without subsidies, a heat pump to replace a fossil boiler is an uphill task for many households without space for all the kit.
Conversely, WTF is our government doing, allowing new-builds with poor insulation and fossil heating? They need to wake up, and stop stroking the nuts of the land-banking big-scale property developers.

 

I think that’s fair points - personally I’m revisiting getting a HP as I’d had a quote which came out as £15k before the grant, however as mentioned this is for an 11kw system, new HW tank, buffer tank, split A2W system and all the work needed to install and new radiators - so £10k or around £3k to keep the existing oil boiler going (new oil tank)

now the grant has gone up to 7.5k im curious as to ways to reduce the proposed HP install - if I could drop the cost down to 3-5k for example after the new grant that would be acceptable I think

 

Monobloc ASHP are the perfect retrofit solution in most cases.
Buffers/volumisers are required if the minimum system volume available to the Monobloc for defrost isn’t quite enough.
The buffer/volumiser can also be configured for hydraulic separation, which could help if there are pipework size flow restrictions in existing pipework.
To produce hot water you’ll need a cylinder compatible with ASHP.
Daikin do a fully pre plumbed cylinder that also has a buffer built into it.
A correctly designed , sized and installed ASHP will work.
You may have to replace a few radiators if what’s already installed doesn’t give the correct heat loss at 55 degrees.
But remember, you don’t have to always replace rads, you can always add an additional one if space allows.
There are many solutions to different situations.

To get more tailored advice I would find an installer that’s MCS Accredited and contact them.
Daikin also support Sustainable Homes Centres around the UK, so you can pop in to them ( like a showroom) look at the kit, and maybe get them to quote you in the process. Details available on the Daikin site.

 

Another question - there seems to be some residential high temp (70 degree plus) HP’s coming to the market which are monoblock and have r290 coolant, presumably then the need to replace radiators is even lower and installation easier than a “standard” HP

downside presumably would be a lower COP, but potentially over time radiators could be upgraded later and the flow temp reduced to improve COP when done

 

HTT units are not Monobloc.

You’ll have the heat pump outside with hydraulic connections that works in conjunction with a hydrobox ( this contains pump, back up heater, filter etc) that’s installed inside.

The secret with any ASHP is the unit being able to reject the heat it produces in a satisfactory way.
Heat Pumps hate multiple stop start cycles , so if you can get smooth heat up, and the maintain its delta T with ease then it will work like a treat.
Low and slow.

 

HTT units are not Monobloc.

You’ll have the heat pump outside with hydraulic connections that works in conjunction with a hydrobox ( this contains pump, back up heater, filter etc) that’s installed inside.

The secret with any ASHP is the unit being able to reject the heat it produces in a satisfactory way.
Heat Pumps hate multiple stop start cycles , so if you can get smooth heat up, and the maintain its delta T with ease then it will work like a treat.
Low and slow.

What are these heat pumps then that are described as monobloc but output up to 75degrees? Is that not a high temp HP?

R290 MONOBLOC DC INVERTER HEAT PUMP

R290 is a fully packaged unit, where the indoor and outdoor units are combined as one module. This unit does not require refrigerant piping work since the Monobloc's outdoor unit is connected exclusively to water piping.

greenpowerstar.com

 

I haven't investigated your particular HTT unit, but they used to be standard technology heat pumps with additional 'heat boxes', which are just heating elements in a tank - hardly efficient or high tech!
The rule of thumb with radiators is this: heat pump circulating temperatures are lower than fossil boilers, so you need radiators to be 3 times as big (in terms of BTU output), or more additional ones.
As for hot water - we have a 300 litre unvented cylinder, set to 55 degrees Celsius. Heating once a day, it's fine for a family of 4.

 

The cost is a problem, but low temperature ASHP are lovely. Remember that to achieve high temperature circulation you need much higher pressure and I suspect that this will have an increased frailty. Low temperature ASHP have the evidence base. Unfortunately to fit them correctly is a considerable amount of work and associated hardware - multiple pumps, DHW cylinder, buffer, expansion tanks, controller etc.
Never looked back after moving from mains gas in a solid wall 1930s home.

 

True, I think sadly if that’s the case and the cost is justified / no real way to cut costs then I’ll have to pause the idea for now as I just can’t justify a £10k outlay on a new heating system right now - especially as in the UK I think the market is still evolving and ever cheaper units/easier installs (eg octopus new heat pump) and likely even better rewards from the government incoming given how far behind the rest of Europe we are with installs - a 0% APR loan secured on the house (so if you sell the house the buyer continues to pay the loan) to be paid off over 10 years for example would go a long way to helping people pull the trigger

 

Apologies. Only used to my companies HTT units

But looking at that unit you’ve quoted, a COP under 3.00 @ 55 LWT.

It’s ok going HTT but if you can hit your heating and hot water comfort levels using a standard low temp unit then why wouldn’t you??

If combined with a load compensating thermostat that reduces the flow temperature once the home is near the target temperature then a HTT capable heatpump can run at a low flow temperature most of the time, so give a good COP if the home is heated 24/7. Likewise with a good control system, even with a normal hot waterr tank, most of the hot water heating cycle can be done at a lower flow temperature then the standard calculations indicates the tank needs.

 

I’m getting my head around the terms but I believe the “inverter” heat pumps are ones which you describe which don't need to turn on and off but instead run at variable speeds depending on how much heat is needed indoors - it seems like a good solution to the “cycling” issue some have and would mean the HP could adapt if you improved your home over time (eg adding insulation, improved radiators)

 

It also need thermostats in each room to tell the heatpump how much heat is required rather then turn the system off when the room overheat.

 

Inverter heatpumps are probably always used now, they adjust the power as needed. Cooler days, so put the heating on this afternoon/ evening, we had 21.5kWh of heat at 25c flow temperature for 2.7kWh power consumption. Tomorrow will be even better with Agile prices, heating off from 16.00-19.00.

 

I have a monobloc heat pump. Mitsubishi 14 kW, dual fan for a 5 bedroom house with 3 bathrooms. It replaced a 30kW Worcester Bosch oil boiler. The boiler was nowhere near the end of its life, for those used to gas, oil boilers can have a life of up to 40 years. And they don‘t need an annual inspection.
The refrigerant is the key to the performance of a heat pump. Mine uses R32 which is more efficient than the previous models by about 15%. Ammonia, CO2 are also used in bigger systems, Octopus are using propane R290 in their new machine. CO2 is interesting because it requires a big difference in the return and output temperatures, perfect for large industrial settings, blocks of flats and swimming pools where a flow temperature of 70 degrees and a return temperature of 30 degrees can be arranged. Octopus haven’t yet published the full spec of their machine but it is said to have a flow temperature nearer to 70 degrees to remove the need for changes to radiators and plumbing in small houses.

My system has a weather compensation system which generally works on a flow temperature of 37 degrees and a return of 33/35 degrees. On cold days the flow temperature will rise to 40 degrees.

I do not have a buffer tank nor a hydraulic separator. The original 28mm pipes contain about 40 litres in the main circuit which provides the heat for defrosting the external hear exchanger. Because we live in the mist on top of the South Downs a larger machine was specified iN order to run the external heat exchanger at a slightly higher temperature so that mist at 3 or 4 degrees, which is common for days on end, didn’t cause the machine to become iced up. It works well but doesn‘t achieve the best COP. But then again, we have 4 pumps, one of which is commercial sized to pump the water around. These consume 350 watts and put a hole into the COP. Tonight it is 11 degrees outside and the heating is drawing about 1400 watts, including the pumps. I think it is common for folks with heat pumps to heat the house to about 20 degrees, comfortable but not over hot. It all works best by just leaving it on, though at this time of the year, I run it hard over night to heat hot water and a 40 m2 slab of underfloor heating. It can be left off for the day and was turned on at 21:00 tonight.
We did not need to change any radiators bar one in a small north facing bedroom which I swapped myself, a single panel for a double panel of the same width. Adding glycol to the water is essential with a monobloc, external pipes though insulated carry a risk of freezing. Glycol has a lower specific heat than water and is also slightly viscous hence the need for more pumps. We do have 18 radiators though, this is a large house by most standards. I wouldn’t swap the heat pump, it has saved a lot of money, we were fortunate to get in before the old RHI scheme closed and we may get £2,000 more back than it cost to put in. It helped that our installer was very local that chopped thousands off the bill, he would pop in at the end of the day to tweak the settings etc and have a final cuppa before he finished for the day.

 

Thanks for your input @Brian G - your setup and the octopus one sounds like the setup I had in mind - one of the newer monoblock heat pumps using r290 that can output a higher flow temp (70-75 degrees)

My thinking is that then we may not need to change HWT nor any radiators at the install which will save money and time, and then over time we can test lowering the flow temp and proactively change any radiators/change the HW tank when we spot any cold spots - as we don’t have underfloor heating I suspect a buffer tank would be wise in our case but one can be fitted where the current oil boiler is located

interestingly since staring this post I had reached out to one company offering to install a powerworld DC power inverter heat pump R290-40 which is detailed here

China Custom Low Gwp R290 Monoblock Heat Pumps Manufacturers Suppliers

We're professional low gwp r290 monoblock heat pumps manufacturers and suppliers in China, specialized in providing high quality OEM service. We warmly welcome you to buy custom made low gwp r290 monoblock heat pumps at competitive price from our factory.

www.powerworldhp.com

The company seems confident that an install of the HP, 100l buffer tank and accessories would be fully covered by the new increased grant - something that surprised me although given the new Octopus system similarly is expected to be mainly covered by the grant now perhaps that’s the way the industry is going with these newer HT heat pumps

 

Thanks for your input @Brian G - your setup and the octopus one sounds like the setup I had in mind - one of the newer monoblock heat pumps using r290 that can output a higher flow temp (70-75 degrees)

My thinking is that then we may not need to change HWT nor any radiators at the install which will save money and time, and then over time we can test lowering the flow temp and proactively change any radiators/change the HW tank when we spot any cold spots - as we don’t have underfloor heating I suspect a buffer tank would be wise in our case but one can be fitted where the current oil boiler is located

interestingly since staring this post I had reached out to one company offering to install a powerworld DC power inverter heat pump R290-40 which is detailed here

China Custom Low Gwp R290 Monoblock Heat Pumps Manufacturers Suppliers

We're professional low gwp r290 monoblock heat pumps manufacturers and suppliers in China, specialized in providing high quality OEM service. We warmly welcome you to buy custom made low gwp r290 monoblock heat pumps at competitive price from our factory.

www.powerworldhp.com

The company seems confident that an install of the HP, 100l buffer tank and accessories would be fully covered by the new increased grant - something that surprised me although given the new Octopus system similarly is expected to be mainly covered by the grant now perhaps that’s the way the industry is going with these newer HT heat pumps

I have come back to this late... The MCS web site should have all the info you need including the spreadsheets to work out your room by room heat losses. I am a mac user without Excel so it gets screwed in 'Numbers' Numbers is pretty but Excel is the real heavy lifter. Valiant heat pumps use R290. Looking at the spec of the heat pumps in your link they seem to have a reasonable COP. The normal standard is measured at 35 degrees flow at 7 degrees outside temperature. Mine is 4.49 iirc. But the real COP includes the power consumed by pumps, which in my case is high. With 18 radiators and towel rails and 40 m2 of ufh we have 4 pumps, one of which is light commercial. Adding glycol increases the viscosity and as I have found 15mm extensions to 2 radiators in new bedrooms above a double garage struggles a bit with the plastic pipe work fittings likely causing disturbances in the flow. It isn't a disaster but one 1200x600 single panel radiator doesn't heat through from top to bottom easily. I have read that plastic pipes should be avoided in the heating systems. My installer had a heat pump to install and he was going to have to tell the client that 30 year old plastic micro bore was brittle and would need to be replaced. However with a pump pushing water into the manifold and flexible 10 mm copper being used it ought to be able to manage radiators up to 800x600 double type 22. At 35 degrees that is an output of 360 watts or thereabouts.
Unlike my old oil boiler the heat pump is clever, it jumps into action and will start drawing 4-5 kW before settling down at 2-3. But in mildish weather it will pump tepid water around all the radiators and ufh and draw 1.3 kW, including 350 watts for the pumps and run at a COP of 4 or slightly better. When the outside temperature is close on freezing it draws 3 kW and runs at a COP of 3.4 Compared to my oil system it is much cheaper to run. If we have a day out and it starts to turn cool I can switch it on remotely via the Internet so no pre timed wasted heat is needed.

 

@Thomas carter
Is your current DHW tank large enough (litres) to meet MCS spec and thus get the grant?
I think the size required is governed by number of bedrooms and bathrooms/ensuites and not by the current number of occupants?

 

@Thomas carter
Is your current DHW tank large enough (litres) to meet MCS spec and thus get the grant?
I think the size required is governed by number of bedrooms and bathrooms/ensuites and not by the current number of occupants?

210L is our current tank size - what’s the MCS requirement for size?

 

Adding glycol to the water is essential with a monobloc, external pipes though insulated carry a risk of freezing.

It can also be done with a heat pump that automatically starts if the temperature in the outside pipes drop too low combined with mechanical valves that automatically drain the outside pipes/PHE if water temperature het near zero.

 

I’ve seen a mention of glycol being an essential in Monoblocs.

Not entirely true.

Water has a SHC of 4.2, a 20% Glycol mix is 3.9.

Glycol reduces the heat output of the heat pump.
A lot of systems get overdosed with Glycol over time, further reducing output.

It’s a simple equation

Q = Flow rate l/s x SHC x Delta T

So take a flow rate of 30l/min.

Q = 30/60 (to get l/s) x 4.2 x 5 = 10.5 kw

Now 20% glycol

Q = 30/60 x 3.9 x 5 = 9.75kw

We recommend anti-freeze valves. Fitted by the Monobloc at the lowest point they open up when the water temp drops to 3 degrees. They then close at 4 degrees.

Water won’t freeze if it’s moving, and our units have protection that brings in the pump if external ambient triggers it.

The anti freeze valves will protect the unit in the event of a power cut.

 

@Badger54
So following a “dump” of water, I assume its just a top-up via a refill loop, like on a gas boiler?
( when ambient rises)

 

@Badger54
So following a “dump” of water, I assume its just a top-up via a refill loop, like on a gas boiler?
( when ambient rises)

Yes mate.

 

Cycling hasn’t been a problem for us with 18 radiators/towel rails and 4o m2 of ufh. We have it zoned between ufh and radiators but don’t often find that it stops one or tother we do notice defrosting which was predicted by the installer to the point he fitted a 14 kW job rather than 11 kW because relying on a much smaller heat exchanger would have it working colder and freeze up more often. We live on top of the South Downs surrounded by trees which slow the wind down at times and leave us shriuded in mist at 3/4 degrees. And that would cause constant de frosting. We have to wash green mould off the brickwork and weather boards every year or so.

 

I assume you know that radiator output can be increased a little by connecting top/bottom opposite side rather than bottom/bottom opposite side. (Flow go into top.)

 

Yep, I’m tboe at the moment, but I think some of them were plumbed up with the flow into the bottom so they’re short circuiting. Something to fix next spring, I’m not mad enough to start re-piping going into December. 🤣