@dchilton David, can i ask why you are installing a heat pump and a gas boiler?

Hi @heacol.

The primary reasons are as a result of the feedback from multiple installers and based on the structure of the building (we spoke to 3). As mentioned above, we live in an old property, with solid sandstone walls (no chance of cavity insulation), high ceilings and we have undergone extensive interior renovations over the past few years so are attempting to keep any internal upheaval to a minimum (i.e. keeping existing radiator system, no changing to internal pipework etc.).

All the suppliers we talked to either stated that an ASHP would not be a good fit for the property without extensive internal works being undertaken, or that a hybrid system was something that we should look into. On top of that, Home Energy Scotland (EST) were offering grants to cover 75% of the cost (of the renewable part of the system at least), with up to a £10k loan, with repayment of the non covered part over 5 years (so in effect, cost to us of £2500 over 5 years).

As we are not replacing the rads, flow temp would be too low, but the principle being that the boiler will then top off the temp if necessary, giving the required flow temp.

Also, my thinking being that worst case, our existing boiler was (a) undersized for the property, so has always struggled, and (b) is on it's last legs, so we are getting a better specked boiler for the property, which should have to work less hard as it is in tandem with the pump. I should also state the pump is for heat only, the boiler will provide DHW.

Basically, feedback we had was that a standalone heat pump was not the best solution for our use case and we have the built in redundancy of the boiler should the pump not cope/fail at any time.

Hope that makes sense and I understand that this is obviously a middle ground type approach which still has a larger than desired carbon footprint, but hopefully a step in the right direction!

Thanks

David

@dchilton hi, if your existing boiler was struggling, a new one will also struggle, and will probably be less efficient as you will be pushing high temperatures, and it will not condense. If you want to improve the situation, you need to do it with intelligence and actually calculate what is required and deal with it. Putting another boiler on, with or without a heat pump, is going to make no differance to your comfort levels and will more than likely be worse on your pocket.

My advice to you, would be to do it properly, upgrade your radiators (even if you only install a condensing boiler) and cylinder.

The heat pump will work fine on it's own, we have installed them in 17th century grade 2 listed buildings with 8mm microbore piping and single glazing, and they work exceptionally well if left to do their job. However, the best place for your Drayton Wiser system is the bin, whichever system you use. Use the manufacturer's controller, the valiant one works well if you use it as an internal sensor. Using third-party controllers just adds another layer of management, nothing works with too many bosses fighting each other.

Your building has a huge thermal mass, if you do not heat it in a way they were originally designed to be heated, (low and slow) it will never perform. You need to use it to your advantage. I much prefer installing heat pumps in old properties with solid stone walls as apposed to new builds. The older properties work much better.

All I can say is good luck, I think you are going to need it if you are not going to do it properly.

@heacol

Hi Brendon,

Well that is a welcome and a half to the forum! 🙂

Thanks for your opinion. I appreciate your feedback and my apologies for not looking at this 'intelligently' and not doing it 'properly'. I am only basing what I am about to do on the advice of 3 separate MCS registered installers, who are proposing to use an official solution, not a cobbled together solution but one direct from the heat pump/boiler manufacturer (Vaillant in this case).

Predominantly the boilers main purpose is to provide hot water (again, without major upheaval we have no straightforward way of installing a HW tank either near to the system, or remote to it without extensive pipe runs and internal disruption) and assist the pump if required. 

On the Wiser system front, in our current situation (boiler only) I can only disagree with you from our in use experience, as having it installed has shown a reduction in the gas usage than without and a more comfortable temperature throughout the house with only those areas which require heat being heated (probably to your point about low and slow, with the scheduling it means the boiler if active more frequently but for shorter bursts to maintain the temp, I have also been able to reduce the boiler temp since installing), whereas before it was a full all or nothing approach. All we have now is more control, which as I say has already started to show real world savings. Whether that remains true when the pump is installed is another question.

Thanks

David

@dchilton As I said, if you are going to install a heat pump do it properly or you are going to be disappointed. If you do not upgrade your radiators, the heat pump will only do a very small portion of the heating or you are going to have an extortionate electricity bill. We are working on a project now, very similar to yours and the home owners electricity bill is over £4000.00 per year. We have repaired many systems where the heat pump has been expected to run at high temperatures (above 45 Deg C), they cannot do it efficiently.

Ask you installer when the switch over point is, what the flow temperature is expected to be at that point, the output of the heat pump in Kw and what the COP will be, this must be evidenced in their MCS heat loss calculations including radiator output at certain external temperatures and flow rates. Do not ask for the SCOP, it is a fictitious figure. I think you may be surprised.

Remember, the output of the radiator is for a full 24 hour period. If you reduce these hours with a timer you will need to increase either the flow temperature or radiator size to make up the shortfall. Usually installers increase the flow temperature.

For your information, every degree you raise the flow temperature from the source temperature (external temperature on an air source heat pump), you raise your electricity bill by 2.5%. This results in an exponential curve and by the time you reach a flow temperature of 40 Deg C, it is very steep and any increase in flow temperature adds significantly to your heating bill.

If you have the actual data, you can make an informed decision, i.e., doing it intelligently.

@dchilton 

I personally designed and built my own system using contract plumbers to complete the installation. I used completely new pipe work, vaillant 637 gas boiler, vaillant cylinder and VRC700 700 control, VRC70 wiring sensor and their ambiense control on the rads with room thermostats in rooms with more than two emitters. I fitted the above with a  Kew to adding the arotherm heat pump at a later date.

I would really recommend the vrc700 vaillant control because it has the ability to integrate with the gas boiler and the heat pump, setting the bivalent point to maximise efficiency of both systems.

@mattengineer, thanks for the useful advice, and welcome to the forums.

@dchilton, welcome to the forums.

Regarding your system, I feel that the central heating world in the UK has gone into binary mode where we now have a choice of fossil fuel boilers versus heat pumps, and it's been portrayed as an 'either/or' situation, which cannot (and should not) be further from the case. 

I believe that houses must decarbonise their heating, but I'll use us an example. We moved onto a property with an oil boiler, and we put in a heat pump, but we retained the oil boiler as a back up. Three years down the line, we couldn't be happier with our decision of keeping a hybrid, bivalent system.

As fuel prices go through the roof, we have the option of switching to oil at times when the heat pump is not efficient. And there's nothing wrong with that, because sustainability must also factor in financial sustainability. What's more, there's a lot of research going into clean fossil fuels. We are looking at running hydrotreated vegetable oils (HVO) to replace our kerosene as an example, and in time green hydrogen may become available, so having back ups and options to fall back on is a good thing. 

Heating is a complex subject, with a lot of moving parts, and there isn't a one size fits all solution out there.

Please keep us updated on your system.

@editor, @mattengineer, thanks both for the comments.

@mattengineer, I am torn at this stage between the VRC700 or the Sensocomfort, so if you have any thoughts as to the best option I would appreciate it, but I believe either would work for exactly the reason you state, to intelligently optimise the balance between ASHP and boiler. Hoping there is some way to integrate the rad control I already have, but if not will bear in mind the Vaillant option (but dont think the Sensocomfort would allow this?!?!? - but if I can play nice with the Wiser system, don't need it! 🙂 ).

@editor, thanks again for the comments. I have recently found your videos on Youtube (and in turn this forum!) and like yourself, part of the reason for the hybrid setup is the flexibility it should provide and agree this is not a black and white world, but am hoping that we are heading in the right direction! Will keep you all updated as it progresses!

Anyway, thanks all

@editor, Mars, I have been working my way through your renewing the conversation series of videos and some really good stuff on there. I wonder if at any point if there are more on the horizon, if bivalent/hybrid systems might get a bit more of an overview (or has this already been covered and I am just yet to find it! 🙂 )

@dchilton 

I have to be honest as a (former)engineer I really liked the modular approach and the scalability of the Vaillant Ambisense system. The vaillant support has always been first class even if you’re a domestic installer and not a plumber. The app control was a big selling point for me especially with a young family, wanting differential temperatures and with working with other heat sources (2 log burners).

I’m tempted to do a little write up on the system, hopefully to fully inform individuals on what the systems capabilities and limitations. 

If you have any questions don’t hesitate to ask.