Heat pump notes

Running costs

Written Aug 2023.

Using resistive electrical heating, our electricity consumption for heating was probably about 10,000 kWh/year.

Octopus tariffs:

Running cost comparison for different methods of heating:

The standing charge for electricity is ignored, since we would be paying it regardless of heating method.
Electricity energy cost is calculated using the average Go rate (30.6*20+9.5*4)/24 = 27.08 p/kWh.

Installers

Heating engineers

These are possibilities for replacing the lounge radiator and servicing the boiler.
I've included rejects as well as possibilities, so that I don't repeatedly investigate the same ones.

Heat pump comparison

Updated Aug 2023

Unit prices exclude VAT and are from Midsummer Wholesale (MW), The Heat Pump Warehouse (HPW), Saturn Sales (SS), City Plumbing (CP), PlumbNation (PN)

SCOP figures for 55°C and 35°C are from Vaillant specification, and are repeated on the MCS site. SCOP figures for 65°C are from extrapolation of the MCS data.

Daikin provide performance data as graphs and also as tables. Unfortunately the graphs and the tables don't agree with each other. The tables are labelled "Rated data for certification programmes", and contain more conservative data than the graphs. Also, the tables contain data for outside ("ambient") temperatures of 7°C and -7°C, but nothing in between. My table below contains data read from the graphs.

Vaillant aroTHERM plus heat pumps

Uses R290 refrigerant.

Three versions:

• with uniTOWER: inside unit integrated 190l hot water cylinder
• with hydraulic module: inside unit with heat pump interface, expansion vessel, back-up heater and divertor valve.
• with heat pump interface: to be used alongside back-up heaters, divertor valves and other heat pump accessories.

Outside unit price:
3.5kW £2673
5kW £2816
7kW £3164

Hydraulic module: about £1000
uniTOWER: about £2000

Table of SCOPs for 5kW and 7kW versions, from MCS:

The last 3 rows of the table are from my extrapolations.

The SCOP for 5kW falls to 2.80 at a flow temperature of 58.7°C. The SCOP for 7kW falls to 2.80 at a flow temperature of 65.0°C. So these are the highest flow temperatures that could be used to be eligible for the BUS grant.

Daikin heat pumps

Written Sep 2024

Octopus are installing Altherma 3 M heat pumps, either 6kW EDLA06E2V3 or 8kW EDLA08E2V3.

SCOP

Table of SCOPs from MCS product directory for Altherma 6kw EDLA06E2V3 and 8kW EDLA08E2V3.

At low flow temperatures the SCOP is much the same for the two heat pumps. At 55°C the 8kw model is 2% better, and at 50°C it's 1.5% better.

For the 8kW model, the SCOP at 55°C flow (3.24) is 7% less efficient than the SCOP at 50°C flow (3.48).

The Daikin specifications have slightly higher figures for the SCOP:

COP

I don't know whether the SCOP figures assume the same flow temperature regardless of outside temperature or if they assume the use of "weather compensation".

Daikin publish tables of max power output HC and input PI for various outside and flow temperatures. These enable the COP to be calculated under various conditions.
This table is for the 8kW heat pump. COPs for the 6kW model are probably similar.
The green cells indicate the optimum states, which hopefully "weather compensation" can achieve (if not, we could presumably set the flow temperature manually).

Heat pump location

Written Sep 2024

At side of house

Distance between side wall of house and next door's garage is 174cm.

Permitted development regulations require 1m between heat pump and property boundary, which leaves 740mm for the heat pump.

Cosy 6 depth is 595mm, so that should meet planning regulations, provided that the gap between the heat pump and the house wall isn't too great.
However, the Cosy 6 apparently needs 2m in front of the wall, presumably for air flow, so Octopus may not allow installation at the side of the house.
If the heat pump needs to 300mm away from the house wall (as does the Daikin), it would project 900mm from the wall and be a major obstruction to the path.

Daikin EDLA0*EV3 depth is 362mm, so that should meet planning regulations too.
It requires 300mm behind and 500mm in front for air flow, making a total requirement of 1162mm - so plenty of room.
Total projection from the house wall would be 662mm, which would significantly obstruct the path.

If a heat pump uses R290 refrigerant (as do Cosy 6 and Vaillant Arotherm), any windows and doors must be at least 500mm from the top of the heat pump and 1000mm from the bottom.

At front of house

The Cosy 6 couldn't be located here as it would be too close to the front door.

The Daikin couldn't go here either: it's 1250mm wide and the wall between the lounge door and the side of the house is onlt 1060mm.

At back of house

A possible position is where the winter jasmine is.

So far as spacing is concerned, either heat pump would be OK.

However, the Daikin (and probably the Cosy 6 too) has a 10m limit on the distance between the heat pump and the hot water cylinder, and the same limit for the 3-way valve. We could be very close to this limit in this position.

Also, the plumbing would have to get past the kitchen door and the gully, which looks tricky.

Hot water cylinder

Capacity needed

See below for MCS recommendations.

A typically quoted figure of water needed for a shower is 80l. Typical water temperature for a shower is about 40°C.

If the mains water temperature is T_m, the energy required to heat 80l to 40°C is 4186 x 80 x (40 - T_m) joules. If this energy was used to heat water to 65°C, the volume heated Vc would satisfy the equation:

4186 x 80 x (40 - T_m) = 4186 x Vc x (65 - T_m)
Vc = 80 x (40 - T_m) / (65 - T_m)

If T_m is 15°C, then Vc would be 80 x 0.5 = 40l (i.e. only 50% of the water used is coming from the HWC).
Our current cylinder is 110l, which should provide enough hot water for 110/40 = 2.75 showers.

If the water in the cylinder was heated to 50°C instead of 65°C, the required Vc for a shower would be 80*(40-15)/(50-15) = 57 litres (i.e. 71% of the water used is coming from the HWC).
To get an equivalent number of showers from a cylinder at 50°C we would need a cylinder capcity of 57/40*110 = 157l.

Fitting in airing cupboard

The airing cupboard is approx 2400W x 950D. Height at front is about 1700mm. Height at back is about 580mm.
Doorway is 530W x 1540H.
The available width W at height H is given by the formula: W = 1514 - 0.95 * H.
The available height H with width W is given by the formula: H = 1600 - 1.06 * W.
The table below gives some examples:

If we moved the airing cupboard wall out we would gain at most 400mm on the available width.

The hot water outlet will be at the top of the cylinder, so we need extra height to accommodate that. For a cylinder of width W, there will be extra height of 1.06/2*W mm available above the centre of the cylinder relative to height at the back. For a typical W of 510 mm the extra height would be 1.06/2*510 = 270 mm, which should be plenty for the hot water outlet.

We need an unvented indirect heat pump 150l cylinder that will fit in the airing cupboard. I have been unable to find horizontal cylinders that meet this specification.

Possible vertical cylinders:

If we remove the block wall, the Geldhill 180l cylinder will fit on the landing, but the Gledhill 210l cylinder won't.

The Gledhill slimline cylinders (PLUHP180SL and PLUHP210SL) obviously won't fit on the landing, but they might go in the kitchen where the boiler is currently.

According to Kingspan the cost of replacing a vented cylinder by an unvented one is £1200-£2500 + VAT at 20%.
A DIYnot forum thread has costs around £2000 inc VAT in 2018 (although one was only £1200).
The building sheriff has cost of £1100+VAT.

Refrigerants

There's some data on GWPs of refrigerants here (link supplied by Bombinho on Octopus forum).

Comments from Bombinho on Octopus forum:

R290 is basically propane, a natural refrigerant. So is R744, which is basically CO2.

Both have the advantage to be barely damaging to the environment. R290 obviously is flammable. But in small devices the amount escaping in the worst case is so small that the dilution in air almost eliminates any such dangers. As well as any early ignition just simply has not much fuel.
Thus I do not expect R290 becoming popular in larger devices. But at the size of domestic dehumidifiers and a2a monobloc heat pumps these are small enough to be considered safe.

On R290 devices you tend to find restrictions in room size. For example my dehumidifier has a minimum requirement of 4sqm floor area. This is to ensure safe behaviour in case of it leaking its limited amount of propane.

R290 devices tend to use a lot less energy than R32, which again tends to be more efficient than R410A. R410A is considered more environmentally harmful than R32, which is considered more harmful than R290.
R744 (CO2) is said to bring amazing results in large industrial devices. Yet I have not seen anything small scale yet. It is considered as not being harmful, due to the amounts released being microscopic and thus easily absorbed in the environment. Though CO2 has its dangers as well, if the concentration in confined spaces gets too high.

Also from Bombinho:

Forget about R32, go for R290, much better suited for small devices. And better for the environment too.

Standard houses

Some statistics from English Housing Survey - Energy report, 2019-20:

• "by 2019 almost three quarters of the stock (74%) had condensing boilers"
  "Local authority dwellings had the highest proportion ... (82%)"
  "private rented dwellings had the lowest proportion 67%"
• "59% of dwellings in 2019 used their central heating system to provide hot water without a separate cylinder"
  "Around a third (32%) used their central heating system to provide hot water through a separate hot water cylinder"
  "7% had a hot water cylinder and immersion heater as the primary means of water heating"
  "less than two percent had an instantaneous water heater or dedicated boiler (1% and 0.2%, respectively)"
• "Owner occupied dwellings had a higher proportion of central heating systems that provided hot water through a separate hot water cylinder (37%)"
  "owner occupied dwellings were less likely to have a central heating system without a tank (57%)"
• "boiler systems with radiators and/or underfloor heating were by far the most common main heating system ... (90%)"
  "Owner occupied dwellings were more likely to have a boiler system with radiators (94%)"
• "gas central heating was the most common heating system (86%)"
  "Owner occupied dwellings were more likely to have gas central heating (89%)"

According to the Green Age "Vented hot water tanks are still the most common type of hot water system found in the UK".

According to Grant UK "In most instances, the coil of an existing cylinder will almost certainly be too small. This will result in longer cylinder reheat times at the lower water flow temperatures from a heat pump."

Regulations

Planning

According to the Planning Portal a heat pump installation is a permitted development, provided that (amongst other things):

the air source heat pump installation complies with the Microgeneration Certification Scheme Planning Standards (MCS 020) or equivalent standards. Read more about the scheme.

The volume of the air source heat pump’s outdoor compressor unit (including housing) must not exceed 0.6 cubic metres

All parts of the air source heat pump must be at least one metre from the property boundary

On land that is not within a Conservation Area or World Heritage Site, the air source heat pump must not be installed on a wall if that wall fronts a highway and any part of that wall is above the level of the ground storey.

The air source heat pump must be:
.....
Sited, so far as is practicable, to minimise its effect on the external appearance of the building and its effect on the amenity of the area.

The definitive wording on planning is in the The Town and Country Planning (General Permitted Development) (England) Order 2015:

G.2  Development is not permitted by Class G if—

(d)the volume of the air source heat pump’s outdoor compressor unit (including any housing) would exceed 0.6 cubic metres;

(e)any part of the air source heat pump would be installed within 1 metre of the boundary of the curtilage of the dwellinghouse or block of flats;

(k)in the case of land, other than land within a conservation area or which is a World Heritage Site, the air source heat pump would be installed on a wall of a dwellinghouse or block of flats if—

(i)that wall fronts a highway; and

(ii)the air source heat pump would be installed on any part of that wall which is above the level of the ground floor storey.

Boiler Upgrade Scheme

According to The Boiler Upgrade Scheme (England and Wales) Regulations 2022 section 3.9.2:

1) A heat pump meets the requirements in this paragraph where—
...
(d) it has a seasonal coefficient of performance of at least 2.8, ...
...

(2) A heat pump meets the suitability criteria in relation to the eligible property, or a property to which regulation 14(1)(b) applies, for which it is installed where—

(a) it provides heating—

     (i) solely to that property, or to both that property and any related property, and

     (ii) for the purpose of both space heating and hot water heating, using liquid as a medium for delivering that heat,

(b) it is capable of meeting the full space heating and hot water heating demands of that property, and

(c) it replaces the heat generating components of the original heating system installed in that property (where applicable), other than any—

     (i) supplementary electric heater, including any immersion heater,

    (ii) circulation pump, or

   (iii) solar thermal collector.

So the heat pump has to be capable of providing all the space and water heating demands - but doesn't actually have to. I.e. the output power of the heat pump has to be at least the total heat loss of the property plus the power needed for water heating.

The heat pump system has to replace the "heat generating components" of the system, except for any "supplementary electric heater". This presumably refers to the gas boiler (not the radiators, since they do not generate heat). But is this why Octopus think they should replace the radiator in the bathroom, unless we convert it to be electrical?

Section 9.1 requires that the heat pumps must meet the following requirements:

(d) it has a seasonal coefficient of performance of at least 2.8, determined in accordance with the standard approved by the Secretary of State under regulation 4(1)(c) which is applicable when the plant is first commissioned,

MCS

The Microgeneration Certification Scheme Standards and Tools Library has several documents on heat pump installation under Installer Standards->Heat Pumps and Installer->Standards->General Scheme Requirements. I've downloaded the most relevant documents on to sage:

• MCS-020 "sets out the MCS Planning Standard which must be complied with for ... installations ... to be 'permitted development'".
• 3 has the planning standard for heat pumps. This is all about noise - nothing to do with visibility.
• MIS-3005-D-Heat-Pump-Design
• 5.5.1(d) specifies internal design temperatures:
  

  Room	Temperature °C
  Living room	21
  Dining room	21
  Bedroom	18
  Hall and landing	18
  Kitchen	18
  Bathroom	22
  Toilet	18

  
  
• 5.5.1(a) specifies external design temperature by effectively referring to CIBSE Guide A Table 2.5. CIBSE Guide A costs £90, but the examples given by MCS suggest an outside design temperature of around -2°C for this location. This would mean a design temperature difference of 23°C for living rooms and bathroom, and a design temperature difference of 20°C for bedrooms and kitchen.
• 5.5.1(e) requires that the heat pump should provide at least 100% of the calculated heat loss without input from any supplementary electric heater.
• where 5.5.1(e) cannot be met, 5.5.2 requires that the output of all heat sources (in a hybrid system) should be at least 100% of the heat loss (note that the Boiler Upgrade Scheme sees to not allow this alternative).
• 5.5.3 says that High Temperature heat pumps should be avoided unless the application requires a flow temperature higher than 55°C.
• 5.6.2 daily hot water demand should be calculated as V = 45 x N, where N is greater of (number of bedrooms + 1) and number of known occupants. For 6 Eddeys this would give V = 135 or 180 litres. This should be used with guidance from MGD 007 to determine cylinder size.
• MIS-3005-IHeat-Pump-Installation
• 5.4.1 requires that only MCS (or equivalent) certified heat pumps may be installed.
• 6.2.2 requires that the installation should allow for heat metering to be added, e.g by installing isolating valves near the heat pump.
• 6.3.6 requires that condensate should be discharged to a drain or soakaway.
• MGD-007-Reference-Information
• 2.1 cylinder sizes recommended by BS 6700: 6kW heat pump with one bathroom 88 litre, 6kW heat pump with 2 bathrooms 200 litre. Table of examples has 1 bath + 1 ensuite 2-3 bedrooms 3 to 6 kW as 210 litres. Note that these are recommendations, not requirements.
• 2.2 has the maths behind the recommendations.
• 4 is an emitter (radiator) guide.
• 4.3 has a method of giving a star rating to the radiators in each room. The star rating is just a way of saying the required flow temperature needed. 4.4 has examples of the star rating, and explains that to get a better star rating you could improve the insulation or fit a bigger radiator.
• 4.5 has a guidance table, which uses the room's specific heat loss (heat loss divided by room floor area) to suggest appropriate action - improve insulation or fit larger radiators. 4.6 has examples of using the table.
• MCS-021 Heat Emitter Guide
  This appears to be an old (21/06/2019) version of section 4 of MGD-007 (14/07/2021).
• Heat-Pump-Guide
  This is a best practice heat pump guide (and is therefore not authoritative for requirements).
  
• 5.1 has guidance on flow rates and pipework sizing.
• 7.1 distinguishes between SPF and SCOP. SCOP refers to performance in a theoretical situation, whereas SPF refers to performance in a specific installation.

Domestic Building Services Compliance Guide

1.7 Work on existing systems
A requirement of the Building Regulations is that work on existing buildings should be carried out in such
a way that when the work is complete:
a. the work itself complies with the applicable requirements of the Building Regulations
b. the parts of the building not affected by the work are no more unsatisfactory in relation to the
requirements of the Regulations than before the work was started.
This means that when a system component like a room thermostat is replaced, only the new component
is expected to comply with the standards in this guide (which in some cases may be lower than for new
systems).