Sense check for ASHP & UFH design

[timhowes]

Thanks to all those who have already assisted me on these topics.

 

We are embarking on a major renovation of an 1949 bungalow, extended through the late 1900s to dormer bedrooms. Building a new first floor with timber construction, extending ground floor a little, adding external insulation to any existing walls, new DG windows and doors throughout. South-westerly aspect without shade. Will have PV and battery storage (not got to work on planning this yet).

 

GF heated area 148m² 

FF heated area 85m²

Total vol approx 600m³

 

Location N Somerset, just west of Bristol

 

I have run Jeremy's heat loss calcs as best as I can, yielding the following (with soil temp 6C, ACH 0.5, no heat recovery)

 

Looking at UFH throughout ground floor - mainly suspended timber and will be able to add plenty of insulation, but small area (kitchen/dining) of existing concrete floor to be extended slightly.

 

Probably FCUs upstairs, although not decided yet, with the intention of some heating if necessary (maybe not needed?) but definitely active cooling,

 

Family of 5 with 3 kids who will be teenagers soon - I am firmly against long showers but their mother is harder to persuade. Envisaging 300L UVC emptying rather fast so considering a larger one.

 

Have been offered plenty of high output heat pumps through MCS-certified installers, with the accompanying eyewatering costs. Trying to get my house in order to challenge them, but also want to know I'm not going to regret going smaller!

 

Questions:

1. I am looking at ASHPs with max ouput 8-9kW based on previous advice from this forum. However my interpretation of the above calcs is that I need to be able to modulate down towards 3kW for efficient running in the less cold months. Is this correct? I've earmarked the Vaillant aroTherm + 10kW model as one option but finding it hard to identify other models with enough modulation (mainly due to poor documentation by the manufacturers - is there an "uber sheet" with these data anywhere?!)
2. Wunda have offered me a 2-zone UFH system for the GF for £4.4k inc VAT - 2 zones needed as, whilst most is suitable for a between-joist system, the concrete floor area needs their "rapid response" to give similar performance. I had asked them for a screed system throughout the GF and need to ascertain why they think their proposal is better. Also sounds like a lot of £ compared to what others have posted. Thoughts? System volume is 148m³

 

As will be evident, I've never done anything like this before and am doing as much reading as I can to defend myself against blowing a big chunk of the budget on an inappropriate heating system!

 

Floor plans attached. Location https://maps.app.goo.gl/acCH67SJ65B4fWmJ8

 

TIA

GAP000 - Level 0 General Arrangement Plan.pdf GAP001 - Level 1 General Arrangement Plan.pdf

[JohnMo]

I would look at Hitachi and HiSense also for their heat pumps. Hitachi and Hisense have a sharing agreement, looking at the datasheet outputs are idenical for each model. But Hisense comes with cooling out the box, Hitachi is an additional cost.  But modulation is great. Neither are that expensive either.

 

13 minutes ago, timhowes said:

2-zone UFH system for the GF for £4.4k inc VAT

Sounds a lot. What is included in that cost

[timhowes]

130m² heated area - mixture of their between-joist system and the "rapid response" overlay for the concrete area, with 150mm pipe centres

 

Designed and supplied as follows:

• Isolation Vales with temperature gauges - pair
• 12 Port Manifold 16mm Pipe
• Actuator Valve
• Smart Hub V4 & Boiler Switch - 48 Zones
• Smart Connection Box V4 - 12 Zones
• V1 - Wunda Thermostat Sensor (Slim)
• Perimeter Strip Insulation - Overfloor (25m Roll)
• 20mm Overfloor EPS 400 Transitional Panel
• 20mm Overfloor EPS 400 Plain Panel
• 20mm Premium Rapid Response Main Panel
• 20mm Premium Rapid Response End Panel (x2)
• Wunda Panel Spray Adhesive
• Joist Insulation Main Panel (200 Micron Aluminium Coating)
• 16mm Wundapipe (80 metre Coil)
• 16mm Wundapipe (100 metre Coil)
• 16mm Wundapipe (120 metre Coil)

 

[sharpener]

33 minutes ago, timhowes said:

I've earmarked the Vaillant aroTherm + 10kW model as one option but finding it hard to identify other models with enough modulation

 

Vaillant FB forum has the famous "Czech" performance charts in the Files tab, shows turndown of all models (which is pretty good).

 

The 10kW is a software limited 12, you might as well have the latter as the min o/p is the same but it would give you faster HW warmup if that is a concern.

[timhowes]

3 minutes ago, sharpener said:

The 10kW is a software limited 12, you might as well have the latter as the min o/p is the same but it would give you faster HW warmup if that is a concern.

 

Good to know - thanks for this.

 

4 minutes ago, sharpener said:

famous "Czech" performance charts

 

This was what led me to the aroTherm - the best data representation of any manufacturer I've seen so far. Why can't they all do this?!

[SimonD]

47 minutes ago, timhowes said:

Have been offered plenty of high output heat pumps through MCS-certified installers,

 

Who have you gone to? Please feel welcome to dm me if you don't want to publish the list in public - that way I can check if you've been to the sensible ones in your area. I can also point you in the direction of an organisation that can assist you in the design process who are also local but not tied to any particular installer.

[SimonD]

18 minutes ago, timhowes said:

130m² heated area - mixture of their between-joist system and the "rapid response" overlay for the concrete area, with 150mm pipe centres

 

Designed and supplied as follows:

• Isolation Vales with temperature gauges - pair
• 12 Port Manifold 16mm Pipe
• Actuator Valve
• Smart Hub V4 & Boiler Switch - 48 Zones
• Smart Connection Box V4 - 12 Zones
• V1 - Wunda Thermostat Sensor (Slim)
• Perimeter Strip Insulation - Overfloor (25m Roll)
• 20mm Overfloor EPS 400 Transitional Panel
• 20mm Overfloor EPS 400 Plain Panel
• 20mm Premium Rapid Response Main Panel
• 20mm Premium Rapid Response End Panel (x2)
• Wunda Panel Spray Adhesive
• Joist Insulation Main Panel (200 Micron Aluminium Coating)
• 16mm Wundapipe (80 metre Coil)
• 16mm Wundapipe (100 metre Coil)
• 16mm Wundapipe (120 metre Coil)

 

 

Best thing to do is step back and look at the heating system as a whole which could allow you to run the system open-loop and allow the heat pump controls to modulate output as opposed to installing a load of control gumpf from the ufh people - a sensible installer would have made this point.

 

Also, if you're thinking about engaging someone to design and install, don't hive off the ufh design to diy and then ask the installer to tack on the heat pump. You need a holistic approach here.

[timhowes]

@SimonD this is all very helpful, thanks. DMing you a list now

[ectoplasmosis]

48 minutes ago, JohnMo said:

I would look at Hitachi and HiSense also for their heat pumps.

 

Apparently Hitachi's parts, warranty and engineer support is almost non-existent in the UK. This would make it a complete non-starter for me.

[JohnMo]

43 minutes ago, timhowes said:

Why can't they all do this

They nearly all do, you just need to search hard as they all call the files different names. Mitsubishi have a excellent data set, for actual UK models, how actuate a Czech data set is for the UK market is questionable. Especially as the data set has models not available in the UK.

[timhowes]

1 hour ago, JohnMo said:

modulation is great

 

Struggling to find a Hisense datasheet which shows modulation capabilities... Trying quite hard!

[JohnMo]

12 minutes ago, timhowes said:

 

Struggling to find a Hisense datasheet which shows modulation capabilities... Trying quite hard!

Its in the brochure, they state the 7 degs min out put for each model

4.4kW is 1.85kW

8kW is 2.1kW

10kW is 3.3kW

etc

They all do just about nameplate rating at -7 outside

 There is a huge technical book tha has all the details as well but I have deleted it

https://solartradinguk.co.uk/wp-content/uploads/2025/01/Hi-Therma-Monobloc-brochure-2024-1.pdf