JamesPa

I think my 2year journey into the world of heat pumps has now reduced to a remarkably similar question. My house has a measured demand of 7.5kW, a calculated demand of 10.5kW using MCS assumptions, and requires 16kW according to two MCS full 3hour surveys who ignored fabric upgrades that they couldn't see. The perfect location technically is on top of my flat garage roof directly above the boiler. I can just squeak in within the PD noise rules with a 60dB unit, which several 10-12kW (single fan - which is a requirement in this location) units are, or I could choose the Vaillant 7kW R290 mono unit at 54dB (claimed) which is good for 7.5-8kW, looks very nice indeed, and will end up a few dB below the PD limit but still 5dB above what my LPA will agree to under express consent. To install the Vaillant I either need an MCS installer who will believe my measured losses and ignore the conventional fabric calculations, or go non-MCS requiring express consent, which means additional attenuation. Even if I choose the former I could still be subject to a noise complaint and, since the environmental health officer has declared his position (namely that he does not accept the PD rules), I fear it might be upheld or at best it will cause grief. Alternatively I can stick more or less any unit I choose (split or mono) some 15m down the garden, avoiding any issues with noise but requiring a 15m-20m trench and removal and replacement of about 10 linear m of block paving. In practice therefore it boils down to Vaillant plus some enclosure/screening on my garage roof, or more or less anything 15m down the garden. If I could create a screen for say £1K which looked sensible on the flat roof and worked structurally, that would probably be my preference, albeit at a risk that the unit would be audible inside my own house, fortunately at a non sensitive location. Perhaps illogically I'm a bit nervous about splits, they seem much less commonly available than monoblocs and often a generation behind, but the thought of running a 15m-20m buried water line doesn't appeal, whereas a refrigerant line is definitely easier (I might even, if I run refrigerant, be able to circumvent digging up the block paving as there is an old drain pipe under the path in question that possibly could be repurposed). Alternatively I could just do nothing and wait until my gas boiler, now about 15 years old, packs up and hope that ASHP technology has advanced enough by then that its all a lot easier. But then it would likely be a distress purchase which is never a great idea. I think most sane souls would have given up by now, but im not a quitter. If I knew there were some technology genuinely around the corner which would help I would wait. Sadly I probably wont be able to get to the installer show in Birmingham later this month to find out!

No I'm not. But I want them to answer the next question I'm going to put to them!

Sorry you are right, I forgot to divide by COP. Trench and pipe costs are still real, but one off. Of course there is an additional loss due to the increase in refrigerant temp needed (and hence reduction in cop) for a given flow temp to compensate for the temp drop due to the heat loss. I don't know the speed at which the refrigerant moves through the pipes, so can't work out if that matters.

Based on what we both conclude it looks like order 200 watts penalty whether it's water or refrigerant in a 20m run. As you say something to be avoided, but not at all costs. Put another way it's about £1-£2 per day when heating, perhaps say £300 per year. That's 15 years to pay for a 4k enclosure. Mind you 20m of trench and insulated pipe isn't cheap, so the enclosure begins to look more attractive when you take this into account. The cost of accoustic screens/enclosures for ashps is quite out of proportion, this needs to come down by a factor if 10. I'm surprised ashp manufacturers haven't done something in this space (I think I read somewhere that Daikin have).

Two 'off the wall' installers have now recommended to me a small cylinder (vented or invented) with no internal coil and a PHE. One suggested putting the small cylinder in the loft, insulated of course, and also predicted that cylinders with coils are history. I am warming to that conclusion, and of course a UVC in the loft has an easy run for the vent. There is more than one way to solve the dhw problem, the painting by numbers guys just aren't there yet (and possibly never will be as many of them are dependent on the plumbing simplicity of the ashp system vendors pre-plumbed cylinder). I have challenged MCS on their system sizing methodology in relation to retrofits. To my surprise I did get a response, and they appear to recognise that there is potentially room for improvement. Unfortunately they declined my request for permission to publish their response. The EPC rules do funny things with the various forms of mechanical ventilation, in an attempt to simplify SAP to the point of idiocy. It may be linked to this.

Which likely means, given that vaillant specs are conservative, that it's plenty big enough but his stupid MCS calculations which rely on far too much unknown data about the fabric don't say so and/or he makes more markup on the viessmann. Seriously I would check against actual measurements!

Vaillant quote about 54dB(A) for their R290 models, but they specify it's at A7W55. I haven't found a 'maximum'. LG quote 60 but then say it might be up to 64. Many others just quote a figure. All this makes me doubt whether the manufacturers are quoting on a like for like basis and/or whether the number in the spec sheet is the number required for the MCS calculation. I have a feeling ochsner might be the absolute quietest, they do horizontal fans in a bulky split at silly prices so I looked at them briefly then discounted

Any idea what the gwp of a can of expanding foam is?

Ok, so attempting to answer my own question, engineering toolbox https://www.engineeringtoolbox.com/heat-loss-insulated-pipes-d_1151.html gives loss curves for insulated metal pipes. If we assume 5/8":3/8" which seems quite common, and say 10-20mm insulation, again quite common, the loss at a delta T of say 40 is around 10W/m. That's not insignificant over a 20m length (X2 for out and back). If these assumptions are even faintly correct then you need a lot more insulation than the standard provided to achieve negligible loss, which makes it a lot less easy to handle. Have I gone wrong somewhere?

Thanks, that's helpful.. Are there, so far as you know, any actual figures for loss eg per metre. I completely understand the practical arguments but obviously the numbers do matter. I calculated 300W penalty for 20m of well insulated water line, that's not insignificant. It would be good to know what the same length of refrigerant line does.

Indeed, that had occurred to me. My calculation assumes insulated pipe in a cold atmosphere, I haven't yet factored into the calculation the insulating properties of wet soil, which will help. I'm yet to find an accessible formula for this.

Can you clarify a bit the rationale. My simple physics says that the refrigerant line post compression must be hotter than the water flow temp so thermal losses are greater, but I must be missing something otherwise what's the point of splits?

I agree with your wife, much better!

Beauty is in the eye of the beholder. Quite a few ashp marketing leaflets feature ashps proudly displayed on a patio or at the front of the house. Generally they also feature modern Germanic/Scandi houses. Personally I think it needs to be aligned with other features so either under the window, centred, or centred on one of the stretches of wall without a window. It might also look better on the wall centred both horizontally and vertically wrt the window or bottom/top aligned I don't personally think ashps are inherently ugly, but like anything else visual lines matter. Almost any feature can look ugly if visual lines aren't resolved. PS I don't personally think hiding it in the current location will work because of the unresolved visual lines. I repeat beauty is in the eye of the beholder.

This is really interesting as it confirms what I had begun to suspect namely that installation under PD rights may not give protection from an action under environmental health legislation. Clearly this is a legislative trap which, as you say, needs to be sorted. Does the complaint arise from winter use when presumably your neighbours have their windows closed, or from summer use. I have argued that an argument can be made for allowing ashps to emit noise above a relatively quiet background, which the pd rules do, on the grounds that they are noisiest when it's cold and people will be indoors with the windows closed. However this argument is invalid in summer when the ashp may still be in use for dhw.

As a matter of relevant interest how far is the pump from your neighbours living/bed room(s), what's the visibility what does the MCS calculation say is the noise pressure at the assessment point() what pump model is it is the area you are in rural and quiet, urban and noisy ore in the middle There is still dispute over whether the permitted development noise standards 'work', certainly the Environmental Health Officer at my LPA doesn't believe in them, and DEFRA have launched an investigation. God help us (and the planet) if the outcome is to make them tighter mind you!

sorry the question was meant for @Jonshine

As a matter of relevant interest how far is the pump from your neighbours living/bed room(s), what's the visibility what does the MCS calculation say is the noise pressure at the assessment point() what pump model is it is the area you are in rural and quiet, urban and noisy ore in the middle There is still dispute over whether the permitted development noise standards 'work', certainly the Environmental Health Officer at my LPA doesn't believe in them, and DEFRA have launched an investigation. God help us (and the planet) if the outcome is to make them tighter mind you!

That's what I did (I think for only 2 years). Sorting into bins is easy. I cant remember exactly how I did it but round(t+0.5,0) rounds to the nearest whole number and then a pivot table on the result (to count) is one method, or you could use a series of countif's

My thoughts (like those of others on here) in relation to heat pumps are pretty well documented in other threads on this forum and I don't think I should labour them. My biggest issues personally are 1. The fact that they have worked their way into permitted development rights so that the use of an MCS contractor (design + install, they cannot be split by the customer) is required if you are to install a heat pump without getting express planning consent, thus effectively creating a near-monopoly 2. The fact that they more or less insist on a method of calculating the system size which, for retrofits, ie their main market, may bear little or no relationship to reality. This wouldn't matter except that system sizing is so crucial to the performance of the system, the cost and the disruption. 3. The fact that their rules are largely about process not outcomes, which protects the installer not the consumer whilst at the same time stifling innovation In fairness to MCS they have recognised (3) in their latest consultation, whether it will change I don't know. I recently challenged them on (2) and today received a response. I intend to ask for permission to publish it as it deserves to be heard. I haven't yet engaged with them in respect of point (1). I should add that I'm just a consumer, not from the trade, albeit a consumer with a background in engineering, a degree in physics and who has spent 2 years failing to get a quote from an MCS installer for a heat pump suitable for my property (I've had plenty of quotes!) and reading the experiences of other on this forum and elsewhere. I suppose one could deploy the 'its early days and work in progress defence', to use software analogy - its still in beta testing. However beta test software is generally declared as such and those who participate do so knowingly and are given meaningful feedback opportunities. In relation to solar PV, my comment was that lots of the early installers went bust when the grants dried up and I am guessing the same will happen with Heat Pumps. Realistically people see an opportunity to harvest some taxpayer cash. Some of those are competent, professional and value their reputations, because they intend to stay in business (feel free to complete the sentence). As to design resources, I cant point at a 'handbook' (others may) but reading on this forum and watching heat geek and john cantor videos will help. If you are designing for an existing property, get a smart meter for your gas (and the ability to download the readings) asap, or take daily fuel consumption readings in the heating season if not on gas. Note any changes you make to the way you use your heating. This will give you an experimental determination of actual load. Then use this information to sense test any system sizing done by spreadsheet. Getting this right is more than half the battle.

Why do you think this has anything to do with joule, it sounds like a problem with the diverter, not the cylinder or immersion. Unless I'm missing something.

This is where it gets difficult. I used daily average temperature for the nearest weather station, this data is freely available. This is going to introduce some error in the calculation the magnitude of which depends on how quickly your house reacts to external temperature changes. Mine is quite slow to react, taking a day or thereabouts to 'stabilise' so I was happy that average temperature was good enough for what I was trying to explore. Degree days are good for some purposes, but probably not this one. Hourly data is available by following links from the met office to another site (I can't recall where exactly). You have to register and can then download about a month's worth for free, any more you have to pay. Im not sure if this is a daily or all time limit.

I agree with a lot of what you say and particularly the issue with a bias against A2A. Having said that self-install single a2a units are available for not a lot of money and to be honest if 1 or 2 is all you need, then its still going to be comparable with a gas boiler without the grant. This being the case I can see an argument for not subsidising them. Making gas more expensive is political suicide of course, which is why the Government wont do it. If it were smart, what it would do is not allow gas prices to drop from their current elevated level as much as they otherwise would do. A judiciously timed shift of the green taxes, which currently fall on electricity, to gas, would not be noticed in the general falling market price. But that requires rapid, intelligent action with a laser focus on the (purported) end objective. I'm not holding my breath!. Much of the current problem, in my humble opinion (based on lots of reading and 2 years of trying to get a sensible proposal out of 'the industry') is down to the grant harvesting industry and their partners in crime, MCS. The (almost) rigid rules imposed by the (almost) unavoidable requirement to have MCS certification (even if you don't want the grant) inhibit the innovation in installation practice which is needed to slash the total install costs and associated disruption. From the point of view of the grant harvesters this is OK - so long as they follow the 'painting by numbers' recipe they are protected from any claim even though the result may be total cr*p. Since many of them doubtless plan to go bust as soon as the grants dry up (as happened in the early days of solar), their reputation doesn't matter to them so long as they are protected from claims. A very small number of installers/specifiers seem to be emerging who are finding innovative ways to comply with MCS but at the same time deliver a cost effective and technically sane solution, however they are currently few and (literally far) between. Octopus are also challenging the model, but focussing it seems solely on a particular class of property.

I think it's possible to do the calculation for a monobloc at least. The distance causes: Heat to be lost - you can calculate how much given the u value of the insulated pipe. I looked up upanor and they are around 0.2 W/mK An increase in flow temp because of the heat lost, assume 2% penalty per degree. A bit more pump power needed I did the calcs for a monobloc based on 20 m run of 32mm water filled pipe with insulation to 150mm dia, buried, and the first was about 400W. This assumes the ground temp is zero, it will be better than this in practice. However the second effect isn't insignificant, at 5kW delivered about 150W. In terms of elec power input the first is reduced by the cop of say 3, so will cause an input penalty of about 140W. Thus the total is about 300W penalty in my calculation. I don't know how this would work out for a split, my gut feel says similar. The refrigerant temp is higher but it might move faster through the the pipe. However this is speculation not physics, whereas the calculation for a monobloc is physics. Incidentally since posting this a couple of real heating engineers (not grant harvesters) have pointed out that a monobloc is possible also in this config which is why I calculated for a monobloc.

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