Boiler-Heat Pump Hybrids

[JohnMo]

https://en.econostrum.info/uk-homes-could-adopt-boiler-heat-pump-hybrids/

 

So at last the UK can use hybrid systems, hopefully with a proper grant. Easy to get the rubbish housing stock to reduce the CO2 emissions by a big margin. No internal heating system changes needed, 80 to 90% of the heating is done by heat pump the cold period by gas etc. No defrosting required on the heat pump killing efficiency and making it more expensive to run.

 

Discuss

[SteamyTea]

1 hour ago, JohnMo said:

Discuss

An environmental disaster, only marginally better than doing nothing.

Not going to be cheap either, and will be abused by many sales orientated installers.

If some are really 'hydrogen ready' then that is environmentally worse than burning natural gas.

 

The only real solutions are to raise the price of energy though carbon taxes and put a supplementary tax on house sales based on kWh.m^-2.year^-1 usage (that data is easy enough to come by).

There is more than enough free equity in the property market to either thermally upgrade or take a hit on the selling price.

[JohnMo]

15 minutes ago, SteamyTea said:

supplementary tax on house sales

That would work for me I'm on about my 10th house. But many just don't move from one decade to the next. So they would just stay as they are, no incentive for the many.

 

15 minutes ago, SteamyTea said:

An environmental disaster, only marginally better than doing nothing.

What makes you say that? Zero need to switch to boiler until it hits about 3 degs. How many days a year do you get below that?

 

15 minutes ago, SteamyTea said:

Not going to be cheap either,

daikin hydro split pump tee'ed to the existing system. Parts just over £2k. No need for a cylinder either.

 

 

[ReedRichards]

1 hour ago, JohnMo said:

What makes you say that? Zero need to switch to boiler until it hits about 3 degs.

 But if you get a hybrid system are you going to bother to change your radiators?  It will seem like too much trouble and expense for many people so that 3 degs might be 10 degs.

[JohnMo]

4 minutes ago, ReedRichards said:

hybrid system are you going to bother to change your radiators

No need, so why would you. You just need a small 4kW heat pump and it tees into existing system.

[JamesPa]

3 hours ago, JohnMo said:

3 hours ago, SteamyTea said:

An environmental disaster, only marginally better than doing nothing.

What makes you say that? Zero need to switch to boiler until it hits about 3 degs. How many days a year do you get below that?

Depends on how it is set up!

 

Since the introduction of condensing boilers the industry has ignored the fact that, to work as designed, they need to be set up with a sufficiently low return temperature that they actually condense.  Why?  Because its easy for the installer to whack it up to max and leave TRVs to sort the mess out.  

 

Any guess what will happen with hybrid systems?  My bet is on installing the cheapest possible heat pump with the most rubbish possible controls, a buffer tank to provide hydronic separation/poor performance, and setting it up so the boiler does most of the work then pocketing any grant available.  Furthermore those of us who have gone for a heat pump risk losing out because the political incentive to fax the electricity/gas price ratio will be reduced.

 

From a purely technical point of view in some circumstances I tend to think its not a wholly bad idea, my concern is the practice.  

 

 

Edited November 24 by JamesPa

[SteamyTea]

I am with @JamesPa on this.

It is the implementation.

Most installs would just plumb in a monoblock ASHP to the heating circuit, DHW would be too expensive to do right as most installs in the last 40 years have been combi boilers.

 

[ReedRichards]

9 hours ago, JohnMo said:

No need, so why would you. You just need a small 4kW heat pump and it tees into existing system.

 

Great.  So you end up with a system that uses 9 kW of gas for every 1 kW of electricity (my figures are guesswork).  That's not really much of an improvement is it? 

[JohnMo]

A paper sponsored by the government 

 

Hybrid_heat_pumps_Final_report-.pdf

[JamesPa]

52 minutes ago, ReedRichards said:

9 hours ago, JohnMo said:

No need, so why would you. You just need a small 4kW heat pump and it tees into existing system.

 

I think the other probable gotcha, based on what we currently see in the market as reported here, is that installers are unlikely to do what you suggest.  They will want to sell a 'hybrid system' complete from a manufacturer.  Bear in mind we are talking about an industry that, as a matter of course oversizes heat pumps and sells us buffer tanks and low loss headers that compromise system performance.  I fear that yesterday's Telegraph article headline 'Now David Miliband wants us to install a boiler and  a heat pump' (or something very similar) actually got it right, albeit for all the wrong reasons.

 

As I say I think the principle is likely OK in some circumstances, I just don't see how our installation industry is going to do a good job given their (lets face it pretty poor) track record and fear it will become just another delaying tactic.

[JamesPa]

Thanks for posting the report which I will read in full.  I skipped to the conclusions and this one struck me as particularly poignant

 

'Heating schedule can also drastically alter the share of demand met by the heat pump component, and could account for some of the variation seen in Figure 8-1. A twice a day heating profile has high peaks in heat demand which require high flow temperatures, and must therefore be met by the boiler instead of the heat pump. This reduces the emissions savings of the HHP relative to a gas boiler. For example, Figure 8-2 shows that the annual emissions savings that could be achieved by a HHP installed in 2017 would be 55% under a continuous heating schedule, but only 18% for a twice a day heating schedule.

 

Obviously the industry will sell the hybrid as being just like a gas boiler, so people will operate it that way, more or less negating the savings!  I fear that the government may be suckered into this by the industry desperate to continue selling gas boilers at any cost to the environment.

 

If they can somehow get it right so that the fears I and others express above aren't realised, then great.  I had read, but have not verified, that some other countries do this, but then other countries have had weather compensation for decades unlike our backward approach!  However if they cant its another nail in the environmental coffin.

[Beelbeebub]

I'd say it's a good thing.

 

The most basic hybrid system just tees the HP into where the boiler F/R pipes with some non-return valves. A control box to fire either the HP or the boiler is then needed.

 

All you need is the HP, probably only a small model 5kw or so.

 

No other changes needed. Boiler handles the DHW via existing cylinder or combi.

 

From a customer perspective there is no risk of the system costing more to run than the gas boiler or performing worse than the gas boiler as their existing system is still in place.

 

If their rads are undersized so the gas boiler has to kick in at a higher temp then they are still saving money, albeit less than they would otherwise. It then creates an incentive - "oh if you swap out these 3 rads, your HP can run more days". They do that and they use less gas. Thry upgrade a few more, maybe a bit more insulation and then the boiler fires only a few times a year.  One day it does and they decide to spend the money of the last few rads and a new cylinder and there we go a heatpump house.

 

 

The onky down side is the capital cost.

 

Appropriate HPs can be a few grand.

 

But if there was a (say) £3.5k grant it coukd end up being nearly free.  The remaining 4k could be for the DHW switch if needed.

 

You coukd even imagine the scheme buying back the smaller 4/5/6 kw units with a few years on them when you exchange for the "final" 8/9/10kw units. Then reselling them at a discount for incoming "hybrid" switches.

[Beelbeebub]

2 hours ago, JamesPa said:

Thanks for posting the report which I will read in full.  I skipped to the conclusions and this one struck me as particularly poignant

 

'Heating schedule can also drastically alter the share of demand met by the heat pump component, and could account for some of the variation seen in Figure 8-1. A twice a day heating profile has high peaks in heat demand which require high flow temperatures, and must therefore be met by the boiler instead of the heat pump. This reduces the emissions savings of the HHP relative to a gas boiler. For example, Figure 8-2 shows that the annual emissions savings that could be achieved by a HHP installed in 2017 would be 55% under a continuous heating schedule, but only 18% for a twice a day heating schedule.

 

Obviously the industry will sell the hybrid as being just like a gas boiler, so people will operate it that way, more or less negating the savings!  I fear that the government may be suckered into this by the industry desperate to continue selling gas boilers at any cost to the environment.

 

If they can somehow get it right so that the fears I and others express above aren't realised, then great.  I had read, but have not verified, that some other countries do this, but then other countries have had weather compensation for decades unlike our backward approach!  However if they cant its another nail in the environmental coffin.

I rent out an old stone cottage.

 

The previous occupant always complained it was cold and damp and cost a fortune to heat.

 

The new tenants say it is surprisingly warm and dry.

 

Now. I did do some upgrades but the biggest thing is how they hear the place.

 

Old tenant was out a lot so would turn the heating off, then come home at 7, turn it on for a few hours so it would run flat out and warm up a degree or two becaue of the massive walls.  It would thnr go off overnight and repeat in the morning. It occilated between 12 and 15C and so was humid as well.

 

New tenants work from home alot so leave the heating at 20.  Turns off overnight where it drops to 18C then climbs again in the morning. They pay a little bit more as the losses are more but they ah e a warm dry house.

[SteamyTea]

6 hours ago, Beelbeebub said:

From a customer perspective there is no risk of the system costing more to run than the gas boiler or performing worse than the gas boiler as their existing system is still in place.

That all depends on how it is commissioned.

We often hear stories of woe on here about peoples heat pumps costing a lot to run, and I am sure many people think that their gas boilers cost a lot to run as well.

 

[JamesPa]

8 hours ago, Beelbeebub said:

I'd say it's a good thing.

 

The most basic hybrid system just tees the HP into where the boiler F/R pipes with some non-return valves. A control box to fire either the HP or the boiler is then needed.

 

All you need is the HP, probably only a small model 5kw or so.

 

No other changes needed. Boiler handles the DHW via existing cylinder or combi.

 

From a customer perspective there is no risk of the system costing more to run than the gas boiler or performing worse than the gas boiler as their existing system is still in place.

 

If their rads are undersized so the gas boiler has to kick in at a higher temp then they are still saving money, albeit less than they would otherwise. It then creates an incentive - "oh if you swap out these 3 rads, your HP can run more days". They do that and they use less gas. Thry upgrade a few more, maybe a bit more insulation and then the boiler fires only a few times a year.  One day it does and they decide to spend the money of the last few rads and a new cylinder and there we go a heatpump house.

 

 

The onky down side is the capital cost.

 

Appropriate HPs can be a few grand.

 

But if there was a (say) £3.5k grant it coukd end up being nearly free.  The remaining 4k could be for the DHW switch if needed.

 

You coukd even imagine the scheme buying back the smaller 4/5/6 kw units with a few years on them when you exchange for the "final" 8/9/10kw units. Then reselling them at a discount for incoming "hybrid" switches.

How much of that do you believe will actually happen.  Liability will stop meaningful reuse of anything and installers will pocket the grant.  We only have to look at what's currently happening to get a flavour of what can, and so probably will, go wrong.

 

Don't misunderstand, I see the argument in principle, but sadly I genuinely can't imagine it being properly implemented in the UK given the starting point (high temperature heating with no wc), the poor level of public understanding and an industry which certainly has many good people but also, sadly, a load of chancers who exist solely to harvest grants.

 

Perhaps any grant should be available to self-installers only!

Edited November 24 by JamesPa

[Beelbeebub]

1 hour ago, SteamyTea said:

That all depends on how it is commissioned.

We often hear stories of woe on here about peoples heat pumps costing a lot to run, and I am sure many people think that their gas boilers cost a lot to run as well.

 

Yeah, commissioning is everything.

 

That said, if the "kit" is just a HP, 2 NRVs and a controller box that either turns the HP or the boiler on depending on what's best. There isn't much to eff up.

 

In the worst case the HP is rarely turned on, in which case the running cost will be no more than if the hybrid system was never fitted.

 

Obviously the customer is out for the cost of the installation (though if most of that was covered they wouldn't even be out for that).

 

Grant harvesting is always going to be an issue tho

[Beelbeebub]

25 minutes ago, JamesPa said:

How much of that do you believe will actually happen.  Liability will stop meaningful reuse of anything and installers will pocket the grant.  We only have to look at what's currently happening to get a flavour of what can, and so probably will, go wrong.

True enough

[ReedRichards]

There really shouldn't be a grant for a heat pump in a hybrid system because it's not doing enough to cut down on greenhouse gas emissions.  If you're convinced it is worthwhile to tack one on to an existing boiler and heating system (and I'm not) then let it pay for itself.  

[Beelbeebub]

39 minutes ago, ReedRichards said:

There really shouldn't be a grant for a heat pump in a hybrid system because it's not doing enough to cut down on greenhouse gas emissions.  If you're convinced it is worthwhile to tack one on to an existing boiler and heating system (and I'm not) then let it pay for itself.  

Though the problem is that it's hard to make HPs "pay for themselves" when the price differential between gas and electric is near 1:4. That said a hybrid system should have an easier job as it can only run when the conditions are such that it can get a CoP of greater than 4:1 and the rest of the time just use gas as per normal.

 

But in carbon terms HPs soundly thump gas boilers.

 

A gas boiler is a bit over 200g per kwh at best

 

Our grid currently provides better than 300g per kwh, often below 200g ie the pout at which direct electric heating is greener than gas boilers.

 

Even *at worst* a HP only has to get to a cop of 1.5 to beat a gas boiler in carbon terms. Pretty much any HP can beat that.

[SteamyTea]

8 hours ago, Beelbeebub said:

in carbon terms HPs soundly thump gas boilers

Yes, and this is what it is all about and is why the the cost of carbon needs to be directly related to the energy source.

8 hours ago, ReedRichards said:

There really shouldn't be a grant for a heat pump in a hybrid system because it's not doing enough to cut down on greenhouse gas emissions.

Yes.  Grants skew the market too much.

[Beelbeebub]

11 hours ago, ReedRichards said:

There really shouldn't be a grant for a heat pump in a hybrid system because it's not doing enough to cut down on greenhouse gas emissions.

On that point.

 

Estimates vary for how much of the demand a hybrid HP would take. 

 

In the better case it's 80% (occupant uses heating system correctly)

 

In the worst it's more like 20% (occupant uses it like a gas boiler ie long periods off, short high power spikes)

 

Say the average is 60%

 

A HP coukd be expected to get a scop of at least 3 of not more (remember it does t give to operate in the coldest periods or do high temps which is where the hit to scop is).  And let's say the average carbon per kwh for the periods the HP operates is 215g/kwh.  It's probably lower as the average is lower but I have assumed the HP is operating more often during periods when carbon intensity is higher.

 

So the carbon intensity of 40% of hearing is 1/3 that if a gas boiler... So overall carbon is about 72% that of a boiler alone.

 

Let's say 1/4 of co2 saved. For a fairly easy, zero risk technical solution.

 

Not nothing.

 

Plus we are getting people used to HPs. Their gas boilers won't last forever. Typically about 10 years before they start to get a bit iffy. 15 years is when thry start to really play up.

 

At that point you could upgrade the rest of the system (DHW). Maybe even just stick a 2nd 5kw unit next to the old one and then you have a 10kw system with really good modulation, redundancy and probably better defrost (can defrost alternately)

 

[IGP]

Depends. They have to be part of a strategy, and a very clear one at that. 

If it’s acknowledging that the skills base for low temperature heating isn’t there and there’s a very clear signal to industry to get their finger out and train and implement low temperature heating design by X date (say 2030 for argument) whilst also decarbonising at the same time and no new gas appliances after 2040. That could fly. 
 

If there’s no explicit strategy, then we have to go through the hard yards upfront in changing the culture to low temperature heating design, but it won’t be pretty. But if we throw hybrids in here, that just makes it worse as it’s extends this messy period where the training and culture of heating design isn’t moving on, possibly an even worse place to be. 

[JohnMo]

Heat pumps like Daikin, Panasonic have inbuilt algorithms where you add tariff, CO2 intensity details and it controls the heat pump and boiler as needed. You need the CO2 output as the default setting and make it difficult to change. The average consumer would have zero interest in changing from the default settings anyway.

 

Looking at Daikin schematic the heat pump is just added to the heating circuit return line, so you don't even need a tee or check valve

 

[ProDave]

52 minutes ago, JohnMo said:

 

Looking at Daikin schematic the heat pump is just added to the heating circuit return line, so you don't even need a tee or check valve

I struggle with the concept of this hybrid arrangement.

 

The basic reason for wanting a hybrid appears to be you have small high temperature radiators and a heat pump can't heat the water hot enough for them.

 

So you add a heat pump to a system with a boiler.

 

I can see in the shoulder months you might be able to run it heat pump only and have lower temperature in the radiators that would work at a time of low heat demand, and add the boiler to the mix when it gets colder.  I could see that working with a changeover either / or situation.

 

But that scheme above with the heat pump pre heating the return to the boiler, assumes the return temperature is low enough for the heat pump to add any meaningful heat to it.  Most boiler fuelled central heating I see the radiators are run too hot to touch, and I very much doubt the return temperature to the boiler is less than 50 degrees.

 

I just can't see this working in a completely automated fashion to add anything of value to the customer.  I doubt the heat pump will ever produce heat cheaper than the boiler.   Why would a customer want something expensive and complicated that saves no or little money?

 

It really sounds like a "box ticking" exercise to get more heat pumps in use, but in a way that is almost guaranteed to get them a bad reputation.

[JamesPa]

3 hours ago, Beelbeebub said:

On that point.

 

Estimates vary for how much of the demand a hybrid HP would take. 

 

In the better case it's 80% (occupant uses heating system correctly)

 

In the worst it's more like 20% (occupant uses it like a gas boiler ie long periods off, short high power spikes)

 

Say the average is 60%

 

 

 

The Government report posted by @JohnMo summarises it thus

 

'Heating schedule can also drastically alter the share of demand met by the heat pump component, and could account for some of the variation seen in Figure 8-1. A twice a day heating profile has high peaks in heat demand which require high flow temperatures, and must therefore be met by the boiler instead of the heat pump. This reduces the emissions savings of the HHP relative to a gas boiler. For example, Figure 8-2 shows that the annual emissions savings that could be achieved by a HHP installed in 2017 would be 55% under a continuous heating schedule, but only 18% for a twice a day heating schedule.

 

So I dont think the average will be 60%, more like 30% because most will inevitably be set up to be and actually used like boilers.

 

3 hours ago, Beelbeebub said:

Plus we are getting people used to HPs.

Only if they use them like heat pumps, otherwise not.

 

1 hour ago, ProDave said:

It really sounds like a "box ticking" exercise to get more heat pumps in use, but in a way that is almost guaranteed to get them a bad reputation.

I fear its an exercise by the fossil industry to perpetuate the use of fossil fuels.

 

15 hours ago, Beelbeebub said:

In the worst case the HP is rarely turned on, in which case the running cost will be no more than if the hybrid system was never fitted.

 

 

In which case there is also no saving in carbon emissions.  Why should any contribution at all to such an arrangement be made from taxation?

 

I think I am for 'no grants' for hybrid systems, other than in extremely rare cases, on the simple grounds that the probability that significant carbon reduction is achieved is too low.  (Unless the integrated control, as @JohnMo says, can be and is locked to the 'minimise carbon emissions' setting and there are penalties for any installer that changes this).  The end game, bear in mind,  isn't installing heat pumps its materially reducing carbon emissions!  Only if this is achieved is the expenditure of any 'public' (in other words our) funds justified.

Edited November 25 by JamesPa