Glad I was sat down!!

[MikeSharp01]

Wonder if @SteamyTea might be up for trawling through all the quotes we have had and doing some analysis to see if it's a y=mx+c and if c = £7500 or just how it scatters.

[peekay]

43 minutes ago, JohnMo said:

Sounds like a bargain, not, but 400L cylinder is a big cylinder, use less zones that are bigger, then get a smaller or no buffer.

 

Would be cheaper to DIY without grant, unless the whole house is being replumped. 

 

Big heat pump, either huge insulated house, or just too big.

 

It is a 5 bed, 280m2 house. New build, well insulated and sealed with UFH throughout.

[sharpener]

36 minutes ago, peekay said:

 

It is a 5 bed, 280m2 house. New build, well insulated and sealed with UFH throughout.

 

I think this is defo over-specced.

 

(5 bed + 1) * 45 is 270 litres so a 300 l tank meets the rules and prob sufficient.

 

Heat Geek say allow 20 - 40 W/m^2 for a post-2006 new build so worst case that would be 11.2 kW. (For comparison, two recent full heat loss surveys for my 200 m^2 uninsulated stone barn have come in at ~12kW)

 

NiBe are notoriously expensive and mandate the use of their pre-plumbed tanks and other quirkiness.

[JohnMo]

1 hour ago, peekay said:

 

It is a 5 bed, 280m2 house. New build, well insulated and sealed with UFH throughout.

Similar build to ours, but we are 195m2 and 3 bed, 210L cylinder and a 6kW ASHP, although max heating load is 3kW.

 

I would be your own heat loss calculations. May have seen big house made up the numbers, you can afford it quote.

[JamesPa]

24 minutes ago, JohnMo said:

2 hours ago, peekay said:

 

It is a 5 bed, 280m2 house. New build, well insulated and sealed with UFH throughout.

Similar build to ours, but we are 195m2 and 3 bed, 210L cylinder and a 6kW ASHP, although max heating load is 3kW.

 

I would be your own heat loss calculations. May have seen big house made up the numbers, you can afford it quote.

16kW will likely be an expensive disaster due to gross oversizing.  Do as @JohnMosays and make your own calculations (or pay someone independent to do them).

[SteamyTea]

3 hours ago, MikeSharp01 said:

a y=mx+c and if c = £7500 or just how it scatters

Most quotes are linear equations.

[Post and beam]

4 hours ago, peekay said:

I've had a quote back that is seems even more crazy

 

-16kw Nibe ASHP

-400l tank

- Nibe UK 200 buffer tank

- install commissioning and MCS Certificate 

 

£21,500 + VAT

 

(Minus the £7.5k grant, so £14k

Was that from Nu Heat by any chance?  My very first 'quote' 18 months ago was from them. Specified by the TF builder. And again mine was very similar numbers.  Apart from the price they proposed 14 heating Zones, one for every room in the house.

Even as a Noob i thought this was total nonsense.

[peekay]

33 minutes ago, Post and beam said:

Was that from Nu Heat by any chance?  My very first 'quote' 18 months ago was from them. Specified by the TF builder. And again mine was very similar numbers.  Apart from the price they proposed 14 heating Zones, one for every room in the house.

Even as a Noob i thought this was total nonsense.

It came through the plumber/heating guy that our builder usually works with, so not sure who the company behind it are. 

 

Previous quotes I've got myself through other companies were a lot less, and based on 12kw systems. 

 

I expect that our builder's plumbing guy would put an uplift on whatever quote they get from a specialist company, but the £21.5k feels like they don't really understand what they are asking for. Not confidence inspiring.

[MikeSharp01]

1 hour ago, SteamyTea said:

Most quotes are linear equations

Yes - I was thinking of just getting all the databank one place and doing some data mining to see if there were any correlations, interesting stuff in it. Suppose we had columns for:

 

Quote value

Area of house 

Number of floors

Heat demand 

Size of ASHP recommended 

Make of ASHP recommended

DHW volume

Number of people in household

Space heating scheme ufh / rads ufh+rads

Number of Zones / Rads

Control system included

Control level simple / WC / full automation.

Etc

 

 

[SteamyTea]

4 minutes ago, MikeSharp01 said:

doing some data mining

Over at the other place, I started a topic where we could enter our weekly household energy usage and house details.

Was quite interesting at first, but people soon got bored and stopped posting up data.

It is probably still on the GBF website.

[JamesPa]

35 minutes ago, peekay said:

, but the £21.5k feels like they don't really understand what they are asking for. Not confidence inspiring.

That and 16kW.  Based on the stories posted here and my own personal experience I would say don't, whatever you do, trust it. 

 

The thing about ASHPs is that the installers interest, when it comes to sizing, is almost diametrically opposed to the householder interest. 

 

For the installer oversizing increases price for little additional effort, justifies a buffer tank and almost guarantees no call outs due to 'its cold'.  For the householder it increases cost unnecessarily and makes poor efficiency highly likely, with a large barrier to fixing it. 

 

Plumbers/heating 'engineers' are used to shoving a 28kW boiler into a 6-8kW house, jacking up the flow temperature so it doesn't condense, and letting trvs sort it all out.  There is an efficiency penalty for this approach, but we are used to it.

 

With an ashp you need to match the size to the demand more closely otherwise you risk a much larger efficiency penalty and having to add a buffer tank (which, unless correctly set up introduces a further penalty) unnecessarily.  People who have been through this, or have spent time on this forum, now understand this.  Sadly there is a proportion of people in the grant chasing (aka installation) industry who either don't, or can't be bothered.

 

You really do need either to do your own heat loss calculations or have someone you trust do them.  Sizing by wet finger wont do and you will come to regret it.

 

 

Edited May 2 by JamesPa

[Nick Laslett]

19 hours ago, LA3222 said:

I installed all mine myself then got spark to wire up. Had to pay a plumber £300 just for the G3 sign off for BC - was at my house all of 30mins checking it over. The beauty if pre plumbed is its a piece of cake...just dot to dot.

This is exactly what I did, inspired by your posts on the topic and the many others here at Buildhub. ASHP isn’t much harder to plumb than a water softener. The challenge is the heat loss calcs and overall design of the system. I spent many hours here absorbing the experiences of others when it come to designing my system. 

[BotusBuild]

Just spoke with someone who seems to be prepared to accept that I know what I'm doing and talking about, and will trust my heat  loss calcs (based on Jeremy's ss). Will report back on what transpires 

[Chanmenie]

Got my quote 

Veismann Vitocal 151-a which has an integrated indoor unit with 190l tank and all the other required gubbins including a 16l buffer, fully installed apart from the concrete pad.

After the BUS of £7500 grant I’ll have just £1800 to pay so chuffed with that.

clearly not all MCS cert plumbers are crooks

[Mr Blobby]

8 hours ago, sharpener said:

(5 bed + 1) * 45 is 270 litres so a 300 l tank meets the rules and prob sufficient.

 

Does this not depend on the temperature of the water in the tank?

With ASHP heating the water to a lower temprature than a gas boiler and all that.

[sharpener]

The HP recommendation from MCS and the tank mfrs trade association is based on 55C IIRC.

 

I don't know what the recommendation is for boilers. Would be surprised if it is more than 60C bc of the risk of scalding. I have mine set to 50 for the oil boiler and 55 for the immersion, so the boiler doesn't cut in if there has been sufficient PV during the day.

[Nickfromwales]

48 minutes ago, Mr Blobby said:

 

Does this not depend on the temperature of the water in the tank?

With ASHP heating the water to a lower temperature than a gas boiler and all that.

Yes, in a nutshell. It was a bit of an over-generalisation tbh and the assumption would better be; at x temp the cylinder has the equivalent heat capacity of stored water @65oC (so at lower temps (~50oC) you need more volume).

[mk1_man]

A couple of things I have learnt on my ongoing heat pump journey is that the heat loss calcs can vary widely. Also they all appear to factor in the heat loss for ground and 1st floors at same time but in reality you generally only need the heat downstairs during the day and possibly some heat upstairs for only a few hours a day, in our case we never have heating upstairs in what is a reasonably well insulated renovated house.  Therefore real life heat loss is a lot less than majority of MCS companies tell you and hence why there are probably so many oversized heat pumps out there.

 

Regarding installation it appears to make no difference to ease of install against cost  i.e. our install is quite simple :  heat pump otherside of cavity wall where boiler is already,  we have existing 28mm flow and return pipes to underfloor heating manifolds, no radiators as underfloor on both, power and 2 core comms already run to where heat pump is being installed as I factored in heat pump sometime in the future so made it ready.  Even with all of this quotes still came in around £8k on top of the £7.5 K grant !

 

I have now gone down the umbrella route of installation and am purchasing and installing heat pump myself along with friendly plumber. All of the paperwork, sign off, grant application is taken care by the MCS umbrella company.  Installation of Vaillant Arotherm plus new cylinder should be cost neutral hopefully.

[SteamyTea]

31 minutes ago, mk1_man said:

Also they all appear to factor in the heat loss for ground and 1st floors at same time but in reality you generally only need the heat downstairs during the day and possibly some heat upstairs for only a few hours a day, in our case we never have heating upstairs in what is a reasonably well insulated renovated house

That should not affect the house heat loss, only the heat emitter's physical locations and power distribution.

[mk1_man]

But it appears to affect the heat pump size required  i.e. the design temp is taken as 21 degrees on both floors at same time. Generally bedrooms are cooler and also not needed during the day, at night downstairs is on setback at around 18 degrees or so.  None of this appears to be taken into account.  I kept trying to argue that what I see day in day out during the winter with my gas boiler doesn't marry up with what I am being told I need on paper. Also MCS forces you to have a warm house at -2 degrees, majority of time temp is not below zero but you are not allowed to factor in the possibility of a few days of the year where you may be a little down on temperature and have to pout on a jumper etc. What that means is the rest of the winter and the majority of the time you have a heat pump that is to big. Bottom line is that I am now installing a much smaller heat pump than I was originally being forced to do, time will tell who was correct 🙂

[JohnMo]

28 minutes ago, mk1_man said:

at night downstairs is on setback at around 18 degrees or so. 

You be surprised how little difference that makes to energy consumption. While you are set back you are using less energy, but once set back has finished the heat pump plays catch up trying to reheat the house for quite a few, using more energy that it otherwise would running steady state. You also have to run higher temps so CoP takes a hit compounding the issue.  "Proton for breakfast" website has a spreadsheet, I tried it consumption was the same setback or not, if the setback was about 4 degrees the setback results in greater consumption, not less.

 

33 minutes ago, mk1_man said:

. Also MCS forces you to have a warm house at -2 degrees, majority of time temp is not below zero but you are not allowed to factor in the possibility of a few days of the year where you may be a little down on temperature and have to pout on a jumper etc.

That's so when you sell the house the next owner can walk about how they like. Take the grant play by their rules, or DIY it.

 

Most heat pumps modulate to below 50% of the max load. They then quite happily cycle 20 mins on 40mins off when needed to run well below min modulation. All normal stuff, if it runs less than about 10 mins, you don't have enough water volume engaged (to many zones or you need a volumiser)

[JamesPa]

34 minutes ago, JohnMo said:

You be surprised how little difference that makes to energy consumption. While you are set back you are using less energy, but once set back has finished the heat pump plays catch up trying to reheat the house for quite a few, using more energy that it otherwise would running steady state

You are of course right.  Many people don't appreciate that the house still loses energy when the heating is off and that energy has to be replaced.

 

There have been several big debates about this recently on the Renewable Heating Forum with people claiming savings of 20% or more (based imho on dodgy assumptions), which prima facie violate the laws of thermodynamics.   There are one or two scenarios where there is a material saving to be had (say >10%) but they rely on a heat pump that is poorly set up (eg way oversized) in the first place or hefty standing loads due to pumps etc ie they are scenarios that don't apply to a well designed system.

 

@mk1_man a very simple calculation to do is to work out the average temperature of the house with setback, over 24 hours, assuming linear cool down and reheat.  So if the heating is on at 20 for 12 hours, and off for 12hrs during which time the house cools to 16C, the average temp of the house is 19C, 1C cooler.  Now if the OAT is say 7C (a reasonable value for the heating season) the reduction in energy lost from the house (and therefore in the amount which must be supplied to the house by the heating system) is 1/13, just under 8%.  With resistance electric heating this will translate to an 8% saving in electricity supplied.  With gas or a heat pump, but particularly with a heat pump, it may be less because the heat pump has to work harder during the reheat period ( equally the saving might be a bit more if the reheat period occurs when it is significantly warmer outside than the setback period). Either way its around 8% so not the game changer much advertising about the advantages of smart controls would have us believe.  Savings from zoning are similarly well overstated by those who sell radiator valves, and with a heat pump zoning can easily lead to increased consumption (depending on the shape of the house).  This is why those who have taken the trouble to understand this stuff advocate avoiding complex control systems and (in most cases) zoning.

 

 

Edited May 3 by JamesPa

[mk1_man]

Thanks for the input.  The thing I focus on more than maybe I should is cycling and the risk of oversizing.  Currently debating whether to install a 7kW or 5kW Arotherm.  The 5kW will probably suffice as majority of time it can generate 7kW  My rational is that it won't cycle as much as possible the 7kW unit will.  Are you saying that a degree of cycling won't harm as long as its not to often?

[JamesPa]

24 minutes ago, mk1_man said:

Thanks for the input.  The thing I focus on more than maybe I should is cycling and the risk of oversizing.  Currently debating whether to install a 7kW or 5kW Arotherm.  The 5kW will probably suffice as majority of time it can generate 7kW  My rational is that it won't cycle as much as possible the 7kW unit will.  Are you saying that a degree of cycling won't harm as long as its not to often?

Others may have some more quantitative answers but I haven't personally seen much by way of concrete numerical evidence here or elsewhere,  other than for some extreme cases.  However there are several very sound reasons to believe excessive cycling should be avoided if possible.

 

It's reasonable to suppose your heating system will spend most of its time at around half the load at the design oat, so a reasonable design approach, it seems to me, is to be reasonably sure it won't cycle at half load (bearing in mind that, at half load, OAT is higher and FT lower, which tends to increase both the max and min output from the pump relative to the values at design oat).  If you can do that its probably around the best achievable with current technology, but it requires knowing the load at design oat to within perhaps 20% (which is why I've been watching my smart meter carefully for two years).

 

It's inevitable that heat pumps (and boilers) will cycle when the load is lower than the minimum.  You can increase the cycle period but adding system volume, but you can't change the on off ratio as this is governed by the ratio of min output to load.  

 

Unfortunately that doesn't answer your 7 vs 5 kW question because of the lack of quantitative data.  The best I can suggest it to decide how accurate your load figures are, and weigh that up against how much you care if for a few days per year you need a little bit of auxiliary heating.  For what it's worth I have decided (if I ever get planning consent) to err, if at all, on the low side, but I'm pretty certain of my demand figures because they are based on measurement reconciled to a spreadsheet calculation.

Edited May 3 by JamesPa

[MikeSharp01]

1 hour ago, JohnMo said:

if it runs less than about 10 mins, you don't have enough water volume engaged (to many zones or you need a volumiser)

Or you need to reset / adjust the delta T or turn it off for a period so the next run will be longer.