Replacing Willis heaters with ASHP - where to source ASHP, what to out look for, how much for install?

[oranjeboom]

It's been a while since I was here. "Life issues"...!

 

Been using the willis heater set up for a couple of years now, and it's proven somewhat more expensive than anticipated, partly down to the electricity price rise fiasco. So I'm now looking to replace the 2x 3kW willis heaters that I had set up feeding the manifold for 150sqm of UFH.

 

More here on my setup: 

 

 

1) Presume the feeds from ASHP will be plumbed in directly to the manifold feed and return pipes, i.e. no buffer tank? I may leave the willis heaters in-situ as a backup. Probably looking at running the temps between 30-40c for 2-3hrs per day (bit more when it's really cold). This is current setup:

 

 

2) Siting the ASHP - the closer the better, but as I'm probably looking at around a 11kW unit, these can be the 'double stacked' types like this, and rather obtrusive to have this next to my front door (closest to plant room). I could site it a bit further out (approx 9m away from entering house) out of view and lay the pipework in the french drain surrounds the whole house - If I had additional insulation to the already insulated pipework would that be an option to consider for an quicker and easier install or would the heat loss still be an issue?

 

3) Can't afford to buy a new ASHP, so looking to get a used/reconditioned one. What are the best places to look at apart from ebay? There are some installers who are selling older but new models that come with warranty still, but any other sources I could consider?

 

4) What should I look out for in a used system? Obviously need to ascertain whether it still works, why it's being sold etc. Ensure that there are no refrigerant leaks, pump works, control board works...

 

5) How much should I look at for an install? I'm happy to dig any trenches, get cabling in by my electrician and do any preparation work to minimise cost.

 

 

Thanks in advance for your feedback/suggestions!

 

[joth]

52 minutes ago, oranjeboom said:

Probably looking at running the temps between 30-40c for 2-3hrs per day

Any particular reason why? Running it for longer at a lower temperature, no more than 30°C, should work out as lower running costs 

[TerryE]

We are in a similar position, in that I am now probably spending about £700-£800 p.a. excess by using the Willis heater at a CoP of 1 rather than an ASHP which should give a CoP of ~4 at 30 °C.  In our case we need about ~30 kWh heating during winter months and I can spread this over the day so I could probably get away with a 5 or 6 kW heat output unit, though these are quite difficult to source.  We also pre-laid our in/out heating pipe to the pad where we would place our ASHP.

 

Like you, I see no point in having a water buffer tank as I don't have the groundfloor space to house it, and we already have a 70 tonne buffer warm slab.  I would rather directly circulate through the slab or poss via a PHE.  I would also prefer to directly drive the ASHP with my own on demand rather than have my control system fight some fancy predictive ASHP CS that is optimised for a conventional house.

 

You need to be aware of planning issues here as you only get a planning consent waiver if the system is installed by an MSCE registered installer who would probably be unwilling to install a config that you want.  Lots of complexities and gotchas here.  

 

And picking up @joth's point 👍.  In my case I would use my existing calibrated slab model the measured out to the slab vs return flow temps to calculate the actual heat input from the ASHP and do a decent block during E7 overnight plus a couple of extra say 2hr heating chunks during the day (if needed) at a ~30°C output set point.  It doesn't really matter if I am ±20% on any day-by-day basis as this only causes maybe an extra ¼°C or so ripple on the overall house temperature.

 

My job over winter is to research all of this and make a call on the way I am going here.

Edited September 27, 2023 by TerryE

[MikeSharp01]

33 minutes ago, TerryE said:

We are in a similar position, in that I am now probably spending about £700-£800 p.a. excess by using the Willis heater at a CoP of 1 rather than an ASHP which should give a CoP of ~4 at 30 °C.  In our case we need about ~30 kWh heating during winter months and I can spread this over the day so I could probably get away with a 5 or 6 kW heat output unit, though these are quite difficult to source.  We also pre-laid our in/out heating pipe to the pad where we would place our ASHP.

Oh well - gone are the days of me pointing people at your Willis system I suppose. I think with the new grant at £7500K you should be able to get it almost free although as you say the unit will be hard to source because modulating a bigger one down to 2.5Kw output will be a challenge. The buffer tank issue is a can of worms as well. We have basically the same slab so I felt I did not need a buffer tank but I wonder how good the heat transfer is and I would want to know that - which you of course do for you place, before I opted for the Free heat pump without one.

[JohnMo]

So you have 2x3kW Willis, confused why you think you need 11kW heat pump?

 

Unless you have poor insulation and are using additional heating not mentioned you should need no more than a 6kW heat pump. Most manufacturers seem to use a lot of common parts on a 4, 6 and 8kW units, but when you get to 11kW you are looking a big unit.

 

A new ASHP doesn't need to cost much, I paid £1300, from eBay.

 

I elected to DIY install and do what I wanted, not be pushed in a direction I didn't want to go, like loads of zones buffers etc. If you can set up a Willis heater, an ASHP should be easy enough.

[MikeSharp01]

I am trying the find the self build grant form any ideas of would an MCS installer know? The 3 month window has me worried is that from when you get sign off or before or after the notice went out it was possible. Any ideas anyone?

[JohnMo]

14 minutes ago, MikeSharp01 said:

trying the find the self build grant form any ideas of would an MCS installer know

 

There isn't a self build form. You just allowed to have the grant.  The MCS installer does all the paperwork and gets the grant, you pay the bills

[Big Jimbo]

34 minutes ago, MikeSharp01 said:

I am trying the find the self build grant form any ideas of would an MCS installer know? The 3 month window has me worried is that from when you get sign off or before or after the notice went out it was possible. Any ideas anyone?

I didn't think there was any sort of grant available for a new self build Mike ?

[MikeSharp01]

1 minute ago, Big Jimbo said:

I didn't think there was any sort of grant available for a new self build Mike ?

It seems there is. I found a couple of places, other than here, talking about it but I could find very little else. @JohnMo seems to agree there is a route. Now all I need to do is find it. I am hoping, as I need such a small device. I have all the plumbing, the base, the cables all in place. So I hope I won't need to find any cash. They turn up, plonk the machine on the base, connect up the pipework, controls, do the commissioning and go away. All done in a day. I bet it costs £7500 though!

[JohnMo]

5 minutes ago, MikeSharp01 said:

bet it costs £7500 though

Bet it cost £12k - they've got to fleece you.

 

Bus info, new build, no you don't get the grant, self build you do.

 

https://www.ofgem.gov.uk/environmental-and-social-schemes/boiler-upgrade-scheme-bus/property-owners

Edited September 27, 2023 by JohnMo

[MikeSharp01]

1 minute ago, JohnMo said:

https://www.ofgem.gov.uk/environmental-and-social-schemes/boiler-upgrade-scheme-bus/property-owners

Yep there it is in B&W great - many thanks, that reassures me. Looks like it has to be finished but that may be up to the installer.

 

[SteamyTea]

48 minutes ago, MikeSharp01 said:

am trying the find the self build grant form any ideas of would an MCS installer know

Did they not announce a new grant, when they decided that climate change was fantasy and we need 300 million more barrels of crude, or was that in Scotland only.

[MikeSharp01]

2 hours ago, SteamyTea said:

Did they not announce a new grant

Yes it is now £7500 for an ASHP as I think our glorious leader told us this when he dumped all the green targets a week or so back. Upping the grant to give more money to the private sector without any accountability that I can see. For instance I cannot see how even earning a very good profit our install could possibly cost £7500 given we need a 5Kw machine at most - we expect to be in about the same boat at @TerryE needing about 2kW per hour at -10 for 20 inside and everything else is already there or will be.

[oranjeboom]

6 hours ago, JohnMo said:

So you have 2x3kW Willis, confused why you think you need 11kW heat pump?

 

Unless you have poor insulation and are using additional heating not mentioned you should need no more than a 6kW heat pump. Most manufacturers seem to use a lot of common parts on a 4, 6 and 8kW units, but when you get to 11kW you are looking a big unit.

 

A new ASHP doesn't need to cost much, I paid £1300, from eBay.

 

I elected to DIY install and do what I wanted, not be pushed in a direction I didn't want to go, like loads of zones buffers etc. If you can set up a Willis heater, an ASHP should be easy enough.

 

8 hours ago, joth said:

Any particular reason why? Running it for longer at a lower temperature, no more than 30°C, should work out as lower running costs 

 

It's costing me too much, simply as that. And the occupants tend to leave it on for too long ("as it's still cold outside...") not getting the concept of a buffer.

 

7 hours ago, JohnMo said:

So you have 2x3kW Willis, confused why you think you need 11kW heat pump?

 

Unless you have poor insulation and are using additional heating not mentioned you should need no more than a 6kW heat pump. Most manufacturers seem to use a lot of common parts on a 4, 6 and 8kW units, but when you get to 11kW you are looking a big unit.

 

A new ASHP doesn't need to cost much, I paid £1300, from eBay.

 

I elected to DIY install and do what I wanted, not be pushed in a direction I didn't want to go, like loads of zones buffers etc. If you can set up a Willis heater, an ASHP should be easy enough.

 

Well, currently still need to do the EWI, so despite 350-400mm EPS under slab, 3G windows, 400mm loft roll and SIPwalls in the new extensions, there is still an unacceptable heatloss. So I think I need a bit more than 6kW and have previously been advised by installers that I'd need at least 10kW. I simply don't want to go down the usual route of undersizing the unit and having to upgrade it.

 

3 hours ago, Big Jimbo said:

I didn't think there was any sort of grant available for a new self build Mike ?

 

Presume this grant only covers new ASHP units? Can we still source new units (say via ebay) and then get MCS installer to fit (at exorbitant cost?). I scanned the BUS blurb but it was not that clear on this.

[Big Jimbo]

No, I can't see that's it's clear. I'm about to start building a new self build. I can't see that a new self build would get a grant. How am I missing it when reading ?

 

[JohnMo]

8 hours ago, oranjeboom said:

So I think I need a bit more than 6kW

Think you need to sit down and calculate the house loss.

 

Oversizing the heat pump can have advantages and disadvantages. It is only an advantage if you are batch charging the floor with off peak electric. Disadvantage it's too big nearly every day of the year and prone to short cycling.

 

8 hours ago, oranjeboom said:

not getting the concept of a buffer

A buffer in simple terms is there to increase the water capacity of a system. So if your min turndown of a boiler/ASHP is 6kW you need around 50L of water engaged to keep away from short cycling (running less than about 10 mins). So if you zone the house in to lots of controlled areas, you take the smallest capacity zone, say it's 30L, then you need to add 20L, this is done with a buffer.

 

There are several ways to install a buffer. 4 port, this requires a pump either side of the buffer and can be prone to mixing of the flow and return water leading to a low CoP. A 2 port can be installed directly in to the flow or return piping or be tee'ed into both the flow and return. A 2 port buffer doesn't require an additional pump.

 

8 hours ago, oranjeboom said:

It's costing me too much

An ASHP, doing long run hours just doing UFH, should yield a SCoP of over 4, so running costs will be 1/4 of your current costs. If you batch charge (E7 or similar), your run hours are less, say 7 hours, but over those hours the CoP is lower (3-3.5) due to higher flow temps, but overall the running cost should be way cheaper.

[joth]

8 hours ago, oranjeboom said:

It's costing me too much, simply as that. And the occupants tend to leave it on for too long ("as it's still cold outside...") not getting the concept of a buffer

If the controls are working then it should be possible, indeed preferable, to leave it "on" every hour of the year, and the system itself manage the buffer rather than the occupants having to understand it. The only control is the target temperature setpoint 

I'd fear a cut price ASHP install might be even more complicated to use and if the occupants  treat it like a combi boiler it'll not give the desired savings.

 

[JohnMo]

A two minute search on eBay, brand new cool energy unit, for around £2k

 

 

[Nickfromwales]

https://www.theheatpumpwarehouse.co.uk/shop/heat-pumps/air-source-heat-pumps/7-kw-panasonic-aquarea-high-performance-mono‑bloc-j-generation-1-phase-r32-wh-mdc07j3e5/
 

Panasonic 7kW for £2.5k + the Vodka And Tonic. Reverses for cooling without much thought / input, but if this is a let property you’d need to decide the merits of cooling (or just not announce it until you perhaps adopt the property later down the road?). 

[TerryE]

We pretty much need two threads here covering the use cases of: 

• The likes of me, @MikeSharp01, etc. who have (near) passive-class houses with only limited heating requirements of say 20-40 kWh heat input / day during winter months.  Here a 5-8 kW range ASHP would be more than adequate.  Here a typical warm slab where the heating loops are embedded in a min 75mm concrete + other concrete ribbing and structural beams can easily soak up 5kW heat, say,  at a ~10 °C delta between average slab and circulating water.  Also remember we only need an average of 1-2 kW input over the day.  In this specific usecase the buffer tank is functionally redundant, and really only required for insulation templates optimised for typical house installations.  My RPi-based control system which computes daily heating requirements based on external weather forecast and actual average house temperature, and schedules heating blocks during the 24hr period to input this into the slab works well here.  
• More legacy installations such as @oranjeboom's, which IIRC is a reasonably efficient extension on a more traditional house.  His heating calcs in this case are even more complicated by the (lack of) EWI and there are all sorts of wrinkles here that need addressing.

I suggest that we keep this topic to orangeboom's issues and discuss these warmslab / passive templates on a separate thread.