We have built a house with the Supawall system - see thread

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6178

and fitted a Nibe F470 Exhaust Air heat Pump to meet or ventilation, heating and hot water requirements.

Nibe decribes the Heat pump as follows:-

http://www.nibe.co.uk/upload/nibe_co_uk/documents/NIBE%20F470%20Exhaust%20Air%20Heat%20Pump.pdf

'The NIBE F470 is a complete heat pump unit for recovering
thermal energy from exhaust air. Warm, oxygen-poor air is
channelled through a ventilation unit which is built into the
system via a heat exchanger located in the heat pump circuit.
The recovered heat is transferred, via a heat exchanger to
a double-jacket tank. The recovered heat is simultaneously
channelled, via another heat exchanger, to both the supply
air and the heating circuit. The hot water tank’s double-jacket
system not only helps to heat the radiator water and domestic
hot water, but also heats the fresh, incoming air. The unit comes
complete with a central heating pump, heating pressure vessel
and filling loop'.

Our thoughts in installing this unit was that it catered for all our needs in what is a highly insulated and hopefully reasonably air tight house, gaining as much benefit as possible from the heat contained within the outgoing stale air on the ventilation side.

First thing to talk about is the unit itself. It measures 600 x 600 x 2100mm or thereabouts. It is also very heavy, and is a four man lift. It is therefore very difficult to manouvere if you are siting it in a confined space / inside as we did.

We had a few issues getting the unit as it was the first one in the UK, due to the previous model being discontinued. When we did get it it was delivered by one man and thus we really struggled to get it inside. The installation took a day and a half to complete. Because a grant can be claimed for having the unit intsalled, the cost of installation was sky high and certainly bore no relation to the limited number of (simple) connections required. The unit was then commissioned by the supplying company which involved both setting up the machine and checking ventilation flow rates.

With the machine on we have a very pleasant internal atmosphere - fresh and never stuffy, constant temperature and plenty of hot water.

It also seems to be working cost effectively. Over the past two weeks our electricity usage with heat pump on has been 856 Kwh, of which 252 accounts for day to day electricity and running the ventilation fans. Heat pump and back up immersion came to 604 Kwh, for a constant 18 - 19 degrees inside 24 hours a day, and all our hot water - 2 showers plus a full bath and misc sink fulls daily. Immersion back up accounted for 347 kwh with the rest being the heat pump.

£52 for two weeks heating and hot water when the temp has been dropping to -10 most nights and not above -2 through the day doesn't seem too bad, especially when compared to to last house we were in - in a similair fortnight of extreme cold weather last year in a new rented house (140mm glass wool walls) we used £250 in gas over a fortnight and it was not even that warm. I accept that this is a crude comparison, but I think we can conclude that the Heat Pump perfoms reasonably well in a highly insulated envelope.

There is a good control panel and there are various changes you can make to the units operation to suit your circumstances / specific electricity tarriffs - e.g. timing hot water operation, blocking operation of back up immersion, adjust fan speed for ventilation flow rates.

We have yet to experiment with the settings to see how much difference there will be. We have meantime decided to stay on a normal tarrif rather than Economy 10, having done a comparison based on anticipated consumption. Our conclusion was that E10 would be slightly more expensive. I am continuing to monitor electricity consumption on a daily basis and will try and update on a regular basis.

If anyone has any questions...

No - all fresh air via mechanical ventilation. No trickle vents in windows. No draughts in windy weather.

Posted By: davidfreeboroughIf you're using a heat pump to extract heat from the exhaust air then the only "new energy" the heat pump provides to the house is the electricity it consumes. In other words, you have a COP of around 3 for energy recycled within the house, but a COP of 1 for new energy introduced to the house.

This is a fallacy. The exhaust air temperature will be below ambient outdoor temperature so the COP will most certainly be greater than 1. Air has heat energy in it all the way down to when it turns to liquid. The heatpump will extract this - the amount extracted, of course, depends on the temperature drop and flow rate of the exhaust air but it will definitely extract energy.

Paul in Montreal

Paul

I take your point, I was over-simplfying my point.

I was trying to get my head around the energy balance. Its relatively straightforward if you have a separate MVHR unit of x % efficiency & a heat pump which takes all of its energy from outside the house. But in this case the energy taken from the air extracted from the house is being used to heat an equal amount of air supplied to the house, provide heating & hot water.

As you point out, the exhaust air temperature can be below the outside air temperature. So you can extract more energy than that required to heat the incoming air to the extract air temperature. I can see how in this part of the energy flow the heat pump can have a COP of 3.

But isn't a significant part of the heat pump capacity being utilised to recycle heat within the house? What proportion of the capacity is left for introducing new energy to the house?

David

Then the element has been on for 26% of the compressor run time and accounts for 57% of your purchased primary energy. So am I correct in thinking that the heat pump only has a COP >1 for 74% of the run time. If so, that doesn't sound that good to me for a heat pump.

Got the following figures taken at 0830 each morning over the past 2 days. I cannot unfortunately break down the figures for when temperature when the heat pump is running & the supply air is being heated while the tank/hot water is not being heated because it is not currently set up to allow me to do so. Additional heating (immersion) comes on to supplement the heat pump when it is required for either hot water or heating.

Sat 18/12 - Sun 19/12

80 Kwh used
Internal temp 17.9
External temp -4.3
Back up Immersion 6.8 hours ( immersion set at 5.3kw)
Compressor run time 17 hours of which 3 hours water. Specified comp output 0.65kw
Extract air temp 16.2
Exhaust air temp -4
Supply air temp 25
Flow temp 44 to air supply battery

Sun 19/12 - Mon 20/12

83 Kwh used
Internal temp 18.4
External temp -4.2
Back up Immersion 7.1 hours ( immersion set at 5.3kw)
Compressor run time 18 hours of which 5 hours water. Specified comp output 0.65kw
Extract air temp 17.2
Exhaust air temp -8.8
Supply air temp 32.3
Flow temp 45.1 to air supply battery

Mon 20/12 temp readings

Internal temp 18.7
External temp -4
Extract air temp 18
Exhaust air temp -7.4
Supply air temp 28
Flow temp 44 to air supply battery

We were averaging 11 to 12 kwh per day in domestic consumption prior to the unit being fitted. The ventilation fans are rated at 25 - 140 watts. We have the ventilation flow set at 55%. Circulation pump rated 100w. A crude calculation gives around a 4kwh daily consuption for the ventilation fans (2 of) and 2.4kwh daily consumption for the circulation pump. We therefore assume a daily consumption of 18kwh. This figure replicates our consumption in previous homes where we have run a MVHR. This figure has not been deducted from the electricity consumption listed.

Assuming a conversion factor of 10.35 KwH to a litre of fuel oil, we have used the equivalent of just under 6 litres of oil to heat our home / DHW. At current oil prices 72p per litre, that comes to £4.32. Electricity use average of 64 Kwh used at 8.66p = £5.36. On face value, the heat pump would appear more expensive than oil to heat our home. However this excludes the benefit of the COP on the compressor side of the heat pump, i.e. what multiple we would have to apply to the amount of oil that would need to be used to achieve the same level of heating / DHW.

Unfortunately, I do not have a similair sized house to compare these figures / anticipated consumption to. I am aware of a couple of SIP houses locally which use wood pellets for heat/DHW, which although insulated to a similair standard, use more fuel in KwH terms (albeit at a similair cost to my anticipated use).

Hopefully David can make something of all the figures above. I have not read the relevant standard to which COP is calculated. I expect that it will be worked out as an average over the year / based on certain temperatures. In the real world, COP will vary throughout the year as the outside temperature varies. It is however clear that the heat pump is extracting heat energy from the extract air in excess of the air temperature itself.

Nibe provides a chart in the instruction manual giving % electrical consumption of the machine each month of the year. Based on this and the normal November temperatures in the UK, I anticipate a total household consumption of 13500Kwh over 12 months. 6500 of that is for domestic electricty and the ventilation fans (which we would have via an MVHR if we did not have this machine) That leaves us with an expected annual consumption of 7000Kwh for the heat pump / Immersion providing DHW and Heating. At current electricity prices DHW and heating would therefore cost me £606 per annum, which stacks up with the anticiapted costs in the EPC (however flawed the calculation is - it was an accurate indicator of both consumption and cost in our previous 2 homes).

Posted By: stonesGot the following figures taken at 0830 each morning over the past 2 days.

Thanks for the data; some interesting numbers.

The first thing to strike me is that even under current conditions the compressor is not running 24 hours. I would have thought it simplest to run the compressor 24 hours & only use the immersion to "top up".

Do you know what determines whether the compressor is running? How is the incoming air heated if the compressor isn't running, does the outer tank act as a thermal store for the duct heater/air supply battery?

What determines whether the immersion heater comes on? Does it normally only operate during the Economy 7/off-peak tariff period?

I'll take another look & let you know what I can deduce. In the meantime, do you know what the air flow rates are for extract & supply in terms of litres/minute or air changes per hour? If the latter, what's the approximate internal volume of the building?

David

Just wondering why the difference between supply and extraction rates?
RobinB

I have fitted the third NIBE470 to be imported.

I am far from satisfied. What the 470 should be described as is a socking great immersion heater with a little heat pump attached. NIBEs sales literature (for the 410, which is essentially the same) says is that the 410 is designed for single and two family house with a heat demand of 4-6kW, and that the immersion heater switches on only when required. It says that at a heat demand of 6.1kW you will get an annual COP of 2.65. It also quotes "savings/year" of 6-8500 Kwh, but since I haven't got a copy of EN255 which this is based on, I don't know whether this is against all electric, gas or oil.

I have recently completed a barn conversion - stone walled barn, dutch barn roof. Internal footprint of about 100sq m. We built a house within the barn, having blockwork cavity walls with 100mm kingspan in the cavity,(avge 0.19W/mK) 125mm below floors (avge 0.14W/mK), whilst the roof is 200mm Warmcel filled within a Paneline box and intello membranes.(avge 0.17) In essence we have a well insulated house sheltered by 600mm of stone wall all round. We have paid great attention to airtightness, although we have not been required to have the building tested. We have installed a woodburner in the living space,(Hwam Monet - expensive but brilliant) which can feed a Chelmer Ecocat tank, which will also be fed by solar when I get it fitted.Whilst this tank can supply loads of DHW, we have built a 600mm deep insulated sand bed into the centre of the house (about 25sq m), and there are underfloor heating pipes set in the sand such that the sand bed acts as a storage medium. All the rest of the house has conventional UFH fed by the 470. The idea is that the sand bed will be charged up using free solar in late summer, and topped up using the by product heat from the woodburner which we light up on winter evenings. We were advised to install the 410/470 in order that the stray, disorganised heat from the sand bed could be captured from the house air, and organised into the rest of the UFH.

The house has been designed to have a high thermal mass, so we've used concrete block walls and beam and block floors. The 470 is in a room outside the barn, which also contains the EcoCat.

Our SAP calcs indicate an annual heating cost of £434pa, and £216pa for DHW, based on an air source heat pump. We rate C75 efficiency, and B83 CO2. A heat loss calculation gives 7.5kw at -3; 6kw allowing for the sand bed being in operation.

We moved in in the middle of the cold spell, but the house had been built slowly, and had dried out over the autumn. However, the sand bed had not been charged up, so that area was a cold spot. I didn't expect the heating to work perfectly from the start, until the house had fully dried, and the sand bed had been at least brought up to the internal temperature of the house.

We have moved to the barn from a 15th century black and white cottage which is adjacent. That has oil fired central heating, and I was used to stumping up about £2500 a year for oil. Our electricity bills were about £250 a year, which covered washing machine, dishwasher, summer cooking (Aga in winter) and the usual lighting, but no immersion heater. We now have all the same appliances, efficient lighting. and induction cooking.

My electricity bill for February (a relatively warm month) was £290. taking £30 off for our normal useage means that the 470 had cost me £260. I thought this excessive and demanded attention from NIBE. Their technician thought that some of the settings were not as good as they could be, and in particular we should not stop the machine using the immersion heater at the 8kw setting - we had limited it to 5.3kw. Particularly he said that the output was 4kw (for £5k!) and that the immersion heater was brought in largely by the outside temperature sensor. We could expect to see it in operation any time the outside temp was below 12 degrees.

We have just been away for a week. That exposes a weakness of the 470. We are used to leaving the house lightly heated when we go away, (10 degrees)to keep out frost, save the houseplants etc, and this makes it all the easier to warm the house up when we return. The 470 has a nervous breakdown if it is fed with air below 16degrees, which in our case means 18 internally to be sure. Since fully heated is 20 in living rooms and 18 in bedrooms, we can't turn the thing down. There is a "holiday" setting, but this is accompanied by a cautionary note, which says if the exhaust air temperature falls below 16, the compressor is blocked (stops working), and the immersion heater takes over. So, turn it down, and you get 100% CO2 rich electrical heating whilst you're basking in the Carribbean. So we left the 470 on nearly full heating (20/18) and with no other use apart from a couple of 12w lights we used 430kwh in a week with mild days and a couple of light frosts. No DHW was used

It looks to me as though this will be about our average use, if we're lucky, and if we use the woodburner on cold nights. Our electricity bill for heating alone will be between 2 and 3 times the estimate in our SAP.

In the defence of the machine, we were also very badly advised over our ventilation ducting. A design was done by a supplier of Polypipe Supertube 125. What this entirely omitted to include was duct insulation. A large proportion of our ducting runs in two service ducts which run outside the internal envelope of the house. Although this duct has 100mm of kingspan above it, and is stuffed with Rockwool, the ducting lies on its floor which spans the wall cavity, so heat is lost there. To get from ground floor to first floor the ducting runs up the cavity for about 1.5m, where it lies against the outer leaf, with a small air gap. The insulation is sculpted around the other two sides. I think we lose a lot of heat there. The total heat loss between the house and 470 is about 2 degrees; more alarmingly, the 470 produces return air at around 37 degrees, and much of this appears to be lost in the ducting. The furthest inlet to the house has had to be closed because in really cold weather it delivers air to the room below the general temperature of the house interior. The NIBE trained guy who commissioned the 470 said it was normal practice to run ducts in cavities, but it's not helped our system. Comfortingly, perhaps, he took the view that the production of warm air was simply a by product, although I'm not convinced.

NIBE say in the instructions that the machine should be connected with flexible ducting with the extract air and outdoor ducts being insulated. Where the machine isn't inside the envelope of the building it's vital to insulate everything.

I'm pleased for Stones that he has cracked some of the control systems. I'm a 68 year old engineer. It's vital that I have a system my wife can run if I keel over. I cannot say I understand the way this thing works, and she never will. It is the most complex piece of domestic machinery I have ever come across, by a long way.

When I embarked on designing and building my house I wanted a heating system with a degree of resilience, in the light of peak oil and under capacity in generating systems. I also wanted economy and least possible CO2 production. The system also had to be automatic for the reasons I give above. Whilst fitting the 470 my plumber was telling me of a customer who was over the moon having fitted an air source heat pump in a 5 bedroom dwelling built just to current building regs, whose total electricity bills were coming out to £450 a year.

I have built a house which surpasses building regs requirements. I feel cheated by a company whose sales literature is so poor that it is impossible to tell what you can expect - in particular, if they said that running consumption was anything like the figures quoted by Stones or myself, they wouldn't sell any of these machines. My next investment was to have been £10-12K on solar PV. I'll get a better return by ditching the 470 and investing in a conventional air source heat pump and a heat recovery ventilation unit.

Cheerio Guys - feel free to tell me where I've gone wrong!

Posted By: DaveHempyardsThe total heat loss between the house and 470 is about 2 degrees; more alarmingly, the 470 produces return air at around 37 degrees, and much of this appears to be lost in the ducting. The furthest inlet to the house has had to be closed because in really cold weather it delivers air to the room below the general temperature of the house interior.The NIBE trained guy who commissioned the 470 said it was normal practice to run ducts in cavities, but it's not helped our system.

It may be standard practice in centralised extract systems, but its a disaster in a system designed to recover heat. Its critical that the extract & supply ducts remain within the thermal envelope & that the inlet & exhaust ducts are insulated. Even within the thermal envelope, insulated supply ducts may also be required to ensure warm air reaches the furthest corners. Air supply below room temperature points to either a loss of air supply heating at the unit or serious heat loss from the supply ducts. So this would be top of my list of things to try.

Posted By: DaveHempyardsI have built a house which surpasses building regs requirements. I feel cheated by a company whose sales literature is so poor that it is impossible to tell what you can expect - in particular, if they said that running consumption was anything like the figures quoted by Stones or myself, they wouldn't sell any of these machines.

The basic problem is that an exhaust air heat pump is seriously limited by the amount of heat available in the extract air. If it reduces the exhaust air to the same temperature as the inlet air then it only provides enough energy to heat the inlet air to the extract air temperature. This only serves to eliminate ventilation losses, provides no net heating & can be done far more efficiently (with an effective COP of >20) by a counter flow heat exchanger.

Additional energy for space heating & DHW can only be gained by reducing the exhaust temperature below inlet air temperature. This is the same for any air source heat pump, but an exhaust heat pump is limited by the volume of air available. Increasing the extract air volume increases the supply air volume which needs to be heated & with low winter temperatures you quickly get into diminishing returns & defrost problems.

Taken together this makes the inlet air temperature critical. If you're looking for a minimum change fix, you have the space outside & you've not finished the garden yet then you could try feeding the inlet air through an underground pre-heater duct.

Posted By: DaveHempyardsMy next investment was to have been £10-12K on solar PV. I'll get a better return by ditching the 470 and investing in a conventional air source heat pump and a heat recovery ventilation unit.

There are some units which use a MVHR type counter flow heat exchanger with an integrated air source heat pump to provide top up heating. This would require a separate solution for DHW, but you could use the boiler stove & solar thermal for that. The downside is that the air source heat pump would typically need to run 24x7. A separate (larger) air source heat pump would allow use of Economy 7 electricity.

One last thought; is the boiler stove room sealed with a separate external air supply? We have an open flue in our living room & even gas fired central heating struggles to make up for the heat lost up the chimney on a windy day.

David

I have one made by a different company and it is the only thing that I have that keeps my house warm. I have very low heat losses (100W for the whole house in October) and there is enough heat in the air to cover the heat losses at least until outside temperatures drop below minus two. It draws 350W of power and seems very efficient. My heat losses in Jan/Feb are only 10% of the OPs.

Trying to get 7.5Kw from a system like this would be unrealistic in my view. the 7.5 would seem to be the problem, are there big areas of glass or major uninsulated areas or breaches of airtightness. I also like anything that gets warm to be inside my thermal envelope.

Just been reading through DaveHempyards experience. I can of course only talk about my own house and how the unit has performed. I have the following figures since installation in Mid November. Household consumption which tallies with our electricity consumption in previous homes (where we had a basic MVHR installed) - 475 kwh per month. Although a high figure this incudes the constant operation of the ventilation fans.

The following figures are therefore exclusively the Nibe 470 consumption - cost of electricity per unit currently being paid 8.66p per kwh

Nov - Dec 1075 kwh used (1550kwh inc domestic consumption) £93
Dec - Jan 1535 kwh used (2010kwh inc domestic consumption) £132
Jan - Feb 2025 kwh used (2500kwh inc domestic consumption) £ 175
Feb - Mar 1525 kwh used (2000kwh inc domestic consumption) £132
Mar - Apr 525 kwh used (1550kwh inc domestic consumption) £ 45

As the weather has warmed up so consumption has diminished. Immersion consumption which is included in the above figures has been as follows

Nov - Dec 604 kwh
Dec - Jan 848 kwh
Jan - Feb 583 kwh
Feb - Mar 800 kwh
Mar - Apr 254 kwh


As previously described our house is very well insulated with an internal footprint 134 sq metres. The Nibe is within the thermal envelop and all the ducting is insulated.

It is disappointing that DaveHempyard is having the problems he is. I suspect that the big issue is the one highlighted - uninsulated ducting. I would agree with qeipl that you need to get to the bottom of why the consumption is so big and the ducting issue would seem to me to be the first thing to investigate.

I am still however experimenting with my unit. In terms of our lifestyle the Nibe suits us as a fit and forget technology, albeit I am trying to tweak things to get it operating that bit more efficiently. As a technology it suits our house and location as we are off the gas grid, and is certainly preferable to me when compared to burning logs/ biomass / oil / LPG. Using SAP figures and fuel efficiencies, I have done paper comparisons against oil / LPG and biomass / logs and have found that for my house there is very little difference in total fuel cost. If anything, the NIBE was working out slightly cheaper to run, without the hassle of burning logs / having to worry about oil / LPG supply as many in my locality did in the cold snap.

The Nibe is not a unit I would fit into a big house and I think the only way it becomes viable is in a highly insulated house.

I therefore agree with davidfreeborough's comment 'Even so, using this as the sole means of space heating requires that the house is to Passivhaus levels of insulation & airtightness. The house described by DaveHempyards doesn't meet that standard'

It seems to me that the unit can either heat or provide DHW in winter but not both without (immersion) back up. It is my understanding that the unit can be coupled with Solar or indeed mated with a boiler or wood burning stove which had been my initial thought ( i didn't hook up my wood burner in the end having been advised against it). This past months figures would suggest to me that as the temp rises, and certainly with outdoor temps above 11 degrees (when immersion use is blocked)the unit can both heat and provide DHW without immersion back up.

The Nibe was only one of two units that did the job I wanted, the other being a Genvex £2000 or so more expensive. Whilst I could have fitted a Genvex as described by David (which I considered) to provide ventilation and space heating, I would still have had to provide a means of heating DHW. It always seemed to come to a choice between installing a secondary boiler (oil / LPG / biomass) which I didn't want to do, solar with immersion back up, night rate electric with immersion back up or go for all instant hot water and no bath (electric showers and instant hot water taps). Lifestyle meant we discarded the last option and the other options seemed to me to raise the overall cost of installing a dual system when compared to the all in one solution that the Nibe offered.

Compared to previous houses the heating / DHW costsa are significantly lower. I would however attribute this to the insulation rather than the Nibe. All the Nibe has provided is a ventilation/space heating/DHW solution at a comparable capital and ongoing running cost when compared to alternatives that would meet our demands and our off grid location.

Hi Jason,

(David J here). Useful info included above. I was interested to see your note about your electricity costs of 8.66p per kWh. Who supplies you at that price? Taking either a straight rate, or with a standing charge, and averaged out, I can't get better than about 20p per unit (allowing for economy 7). Have you not included for the standing charge?

Also, our annual total elect usage will be about 3500kWh. That of course does not allow for solar panels, and log burner with back boiler (both mainly for DHW). Your numbers look like you might be up at 8000kWh or 9000kWh per year?

Making lots of assumptions about same room temps/DHW usage, which is not unreasonable as have similar size families.....

....assuming my 20p per kWh (just for rough numbers, until I change to your 9p supplier), that's £1000 per year contibuted by solar and log boiler ((8500 - 3500)*£0.2).

I don't believe the solar and log boiler contibute that, so there is some way that your set up is consuming a lot of electricity. Looking briefly at your numbers, you use about 3000kWh annually for the Nibe, and 6000kWh for other elect. The 6000kWh for other looks really high - makes the 3000 for the Nibe less of a concern.

As discussed previously, I would definitely reduce your air change rate, but the first area to look at, for me, would be the 'other' elec - maybe a couple of clip-on meters (about £30 each), to see where that 6000kWh is going?

Cheers, David.

Hi Jason,

when I get a little more time, I'll go through you're notes in more detail, cause I really feel that 11500kWhr/yr is a lot (maybe it's not). The 5500kWh/yr for heating is 1000kWh/month (heating months) which is 35kWh each day, or a 1.5kW elect fire running non-stop. I'll dream about it some more...

As for the elect costs - I'll e-mail you a little cost calculator I made up last night (excel), which plots graphs of total annual costs v's energy consumed (for any unit rate values you want), and compares two sets of rates.(eg. standard against Economy7)

It shows that my Eco7 rates versus your EDF rates breaks even for me at 3500 kWh/yr, assuming 20% night usage (which it currently is - intend to move more to night time)

I reckon that you should be able to have 25% of your power usage at night (easily)...

Using your figures from above...

2000 vent&DHW - 75% at night by heating water at night - so that's 1500
5500 heating - 30% at night - so that's 1800
4000 other - some will be at night, but let's ignore that

So of 11500, you could use 3300 units at night (with very little lifestyle change) - that's nearly 30%.

By putting on dish/clothes washes when you get up in the morning, etc, you could drive that further.

So you'd actually be better off on Eco7 after 2500kWh/yr

You can pump in the numbers yourself to the spreadsheet (when you get it), and try different ratios of day/night usage - it takes seconds, honestly!!

Regards, David.