electrical use profile – ground floor power

I have progressively looked at how we use power on the ground floor. This circuit, along with all others in the house, is sub-metered. A review of the data from all sub-circuit meters showed that the ground floor and lower ground floor, combined, were responsible for some 50% of total electrical energy use (see previous post).

The chart below shows the proportional distribution of power on the ground floor as it currently stands. This data is taken from additional plug-in meters on some key-use sockets, which have been installed since November 2014. As we run two small businesses from home, much of the power is related to IT on this floor. The ‘study’ and ‘studio’ represent the two business areas, which together are responsible for around 40% of the use on this circuit. IT servers and comms equipment are powered from a central point, and this adds a further 23%. Broadly speaking, we could say that 2/3rds of the power use on the ground floor is related to IT equipment – 85% use of which is business-related; 15% for recreational (browsing, etc).

GF Socket profileWhat still jumps out at me is the amount (currently 23%) for TV equipment, namely a small 22in Philips TV and a Virgin V+ box. This is the only TV equipment in the house: we don’t watch that much. So why are these two bits of equipment responsible for so much use. The plug-in meters have only been in since November 2014, and we had made some interventions before this point, so the proportion (pre-November) would have been significantly higher than 23%. The chart below shows the daily average profiles for three key months over the last year and illustrate the interventions made.

GF Socket daily profile

Bands 1 to 7: 1, 2 and 7 are overnight, 3 and 5 are working hours, 4 is lunch break, and 6 is evening.

The green line represents July 2014. This is the baseline: using IT and TV equipment without any specific intervention to reduce energy. In August I plugged in a time switch to switch the Virgin V+ box off between 0200hrs and 1600hrs (we never watch or have anything set to record during these times). The benefit of doing so is shown in the September 2014 profile (blue) in band 2. Also in August, several local drives were replaced with two main server drives – the difference in power use in bands 3 and 5 shows that the new equipment is less power hungry (≅80 kWh/yr saving).

In January 2015, the Philips TV was added to the timer circuit, and the timer adjusted slightly (0200 to 1700 hrs). This is shown by the purple line for February 2015. Now the TV and Virgin V+ box both switch off for 15 hours in every 24, and this translates to 140 kWh/yr for the V+ box and a further 100 kWh for the TV: a total of 240 kWh/yr, around £35. The £5 timer has paid for itself in less than two months! Why does the TV equipment use so much in standby? Hopefully, the new EU Ecodesign Directive will have sorted this out for future replacement equipment.

The chart shows our current baseload (band 2) as 34 Wh (2.8 Wh/5mins), or 0.8 kWh/day (300 kWh/yr). This is due to the broadband router (which can’t be time clock controlled) and server equipment in standby/eco mode. At £45/year, we may need to accept that this is as good as it gets. May be Virgin will bring out more energy efficient equipment in the future (V+ box and broadband superhub): if not we may need to consider alternatives.

Overall, whether due to specific interventions, or down to incidental benefit of replacing equipment, the energy savings from this one circuit is forecast to be around 320 kWh/year, approximately £48 – a 10% reduction on our total electricity use.

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electrical energy use

The sub-meters that were installed (see earlier post) have been sending data every 5 minutes to the data logger for the last 18 months. Regular analysis of this energy data has allowed us to start optimising our energy use. The chart below shows the recorded energy use for each electrical circuit (click for enlargement).

Annual Electrical Profiles

The green coloured stacks show the lower ground floor socket circuit, and purple is for the ground floor sockets. These two circuits were responsible for over half our annual electrical use (2014). Given that we operate two separate businesses from home, the ground floor circuit (mostly IT and electronics) did not ring too many alarm bells at first. However, there is room for some efficiency here – additional plug-in meters for individual equipment have been fitted, and results from this investigation will be posted shortly. A closer look at the lower ground floor showed that a fridge freezer (which we inherited with the house) was responsible for nearly 60% of the consumption of that circuit (15% of total electricity). We made a decision in October 2014 to retire the old fridge and replaced it with a new efficient A+ model. Whilst it has made a significant improvement, in hindsight, we should have gone for an A+++ model. Although an extra £150 to buy, the payback from additional energy saved would have been a similar 7-8 years as with the A+ model. But then A+++ model availability is fairly limited right now, and A++ unit payback (similar purchase price to A+++ but greater model choices) wasn’t worth it in payback terms (9-10 years).

The blue colour on the chart shows the lighting energy use, which varies as expected across the seasons. However, November 2013 to February 2014 showed a higher than expected energy use for lighting, so some changes were made:  changing over a couple of regular-use lamps to LEDs, and being more economical with use. The reduction in energy use 12 months on (November 2014 to February 2015) is fairly evident – approximately half the amount of energy used. Except for the MVHR circuit, the remaining circuits are limited in their ability to be further optimised. The MVHR unit used a total of 290 kWh in 2014, which is within expectations. It has just been re-commissioned, which resulted in some fan speed adjustments to slightly lower settings, but this summer we may also look to switch it off for some periods when windows are open.

The dotted blue line shows the total electrical energy use trend over this period. We are on a downward trajectory, which is good. Our total electricity for 2014 was 3240 kWh – a 21% reduction compared to pre-retrofit use of 4120 kWh (nearer to the UK average household for 2013 of 4170 kWh¹). The aim is to get the annual consumption comfortably below 3000 kWh – a  further 10-20%, which looks to be achievable.

¹ Energy Consumption in the UK (2014) – Department of Energy & Climate Change
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post retrofit energy data: the first year

Total Energy Use_1

The chart shows a summary of our measured energy use over the last 12 months for gas and electricity, compared to energy the first (base) year that we were here, which spanned a cold winter (2010_11). Over this period we used a huge amount of gas: 24,367 kWh (typical consumption for an older home is 20,500 kWh/annum¹). The split between heating and hot water was estimated² as 89% and 11% of total gas use respectively, and equates to a specific heating consumption of 140.3 kWh/m²/yr. The comfort in the house was poor that winter and the old heating system really struggled to keep the house warm.

Now fast forward to the last winter 2013_14³, which was comparatively mild, but the reduction in space heating and total gas use is quite striking. Total gas use has reduced by almost 80% compared to the base year, and space heating has reduced by almost 90%. Total gas consumption was 5300 kWh for the year, with proportions being 47% for space heating, 47% for hot water and 6% for new gas hob. The specific heating energy for the last year was 13.1 kWh/m²/yr, which comes in a touch below the Passivhaus target of 15 kWh/m²/yr.

Weekly Degree days

The chart above shows the weekly gas meter readings (total gas) with the degree days overlaid (blue line). Put simply, heating degree days give an estimate of the amount of heating energy, calculated using local, historic weather data. The chart shows a very close fit between the degree days and heating energy use for the first winter (left side of chart). Moving toward the right shows how the gas has progressively reduced (note yellow areas denote when gas was decommissioned during construction: meter reading substituted for electrical heater meter readings). Most striking is the comparison between the last winter of 2013_14 to the winter of 2010_11.

In acknowledgement that it was an unusually mild winter, I have carried out a degree day assessment to determine the amount of heating that would have been required in a cold winter (using the long, cold winter of 2012_13 for the assessment comparison). The results of the assessment for this region, estimate that 21% more heating energy would have been required. This would increase our specific heat demand by 2.7 kWh/m²/yr, to 15.8 kWh/m²/yr – refer back to the right-hand column on the top chart ‘2013_14 DD adjusted’. This revised value is a little above the maximum for a Passivhaus, but is much lower that the maximum allowed for a Passivhaus retrofit (EnerPHit), which is 25 kWh/m²/yr.

There is still a little more thermal work to do beneath the house (insulation and airtightness), so hopefully we will continue to make reductions. But we are very pleased with the results so far. Or, as one of our neighbour’s put it: ‘snug and smug’!

Electrical energy has reduced by 17% compared to the first year, although we still have some further efficiencies to make. All lighting is now either LED (approx 50%), or a mix of compact and linear fluorescent, which is the main measure so far. But, we added an MVHR ventilation system as part of the retrofit, so a 17% overall reduction is not too bad right now.

More details will become available shortly, particularly for electrical energy use, which is fully sub-metered. At some point I hope to be able to do some in-depth analysis on the gas use to measure, rather than estimate, the proportions for heating, hot water and cooking. But, with an annual gas bill of C.£200, it is difficult to justify spending the best part of £1000 to buy and fit the monitoring kit and pulsed meters to do this.

1. Source OFGEM: Typical Domestic Energy Figures.
2. Estimate based upon average of weekly summer gas readings multiplied by total weeks/year.
3. Analysis for years 2012_13 has not been included in chart due to  construction activities.
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backblog #2: mvhr system commissioned

 Paul Novus300 Commissioning in progress

The heat recovery ventilation system has been running for some three months now. The system is a Paul Novus 300 unit, which has a heat recovery efficiency of up to 94%. The system commissioning included balancing the supply and extract air flows and setting the fan speeds for each setting. This all went well and the system balanced well (which isn’t always the case). The photo above left shows the ventilation unit set within a cupboard within my new office. With all the attenuators on the ductwork (see earlier post), and the sound insulation around the cupboard, the system is almost silent: audible only in boost mode.

The photo above right shows the commissioning taking place. The total air flow was measured and adjusted through the intake and exhaust terminals (outside) to ensure total design air flow was achieved. The internal terminals within each rooms are then measured, adjusted and-re-measured to ensure each room receives the right air flow.

More performance data will follow on future blog postings. Keep checking back.

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backblog #1: loft insulation

I have been neglecting this blog and now have a backlog of stuff to update. So, resuming with the loft insulation (and ventilation ducts in the loft)…

Skip full of itchy stuff empty loft

The old glass fibre insulation was stripped out of the loft (lovely job), leaving only the original (pathetically thin) layer of granulated vermiculite insulation. I couldn’t see the point of removing this, so it was left in place. Once cleared and cleaned, the loft was ready for the MVHR duct installation.

Supply and extract risers boxings

The Lindab SAFE ducting is installed approx 200mm above the ceiling (100mm joist + 100mm tie beam). This puts the top of the 100mm ducts approximately at the top of the proposed insulation layer. As these ducts form part of the insulated envelope, I feel it is necessary to create MDF boxings, or shutters around the ducting to allow the insulation to envelop the ducts completely: 300mm to the sides and above, giving some 600mm of insulation to the loft in these areas. The photo above right shows an example of the boxings prior to the insulation.

Warmcel stack  blowing machine

We have used Warmcel for our loft insulation. This is 100% cellulose (recycled newspaper). A total of 85 bags have been installed using a blowing machine.

Warmcel installation

Finished insulation

The photo above shows the finished insulation, in and around the ventilation duct boxings. The boxings account for just over a third of the loft floor area and therefore the area-weighted U-value for the loft is now 0.10W/m².K, compared to 0.13W/m².K if the entire loft insulation was just 300mm deep.

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opening for Bristol Green Doors


We have been busy with (the almost) finishing touches, just in time for the Bristol Green Doors event taking place this weekend (28th and 29th September). So if you’re in Bristol, please feel free to join one of our tours, which run at 1100, 1300 and 1500hrs on both days. We need to limit numbers, so please book – you can do so by leaving a comment on this posting.

More details about the finishing off soon, I promise!

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reader’s request: more information on window fitting

I received a request for further information about how we fitted the windows to minimise thermal bridges. So here goes:

Window fitting stage 1

Each window unit has been fitted into an external structural timber frame, or sub-frame. The sub-frame is standard C16 grade timber and doesn’t need to be tanalised as it shouldn’t become wet within the insulation layer. The size of the timbers in this case were chosen to be 60mm deep for reasons outlined below. The first timber fitted is the sill piece to act as a ledger to support the window during positioning and alignment. The window unit is fixed back to the masonry using nail plates, but most of the weight of the window is on this ledger, so it must be a good fix. The other three sides of the sub-frame can then be fitted snugly around the window:

Window fitting stage 2 Window fitting stage 3

In our case, the surrounding masonry was treated with a slurry (sand/cement) render base coat, to act as the primary air barrier. So, once the windows were fitted and the render had dried, we could deal with the airtightness sealing – sealing the window to the sub-frame and the sub-frame to the wall, using proprietary air sealing tapes. In hindsight we made an minor error here. We should have taped the sub-frame to the masonry and then rendered over the top of the render layer tape (black tape).

We chose 60mm deep sub-frame because we were using 2 x 60mm layers of insulation. The thickness of the window frame is 78mm. So the idea was to have the first layer of insulation run into the side of the sub-frame and the second layer would fly across the face of the window frame by around 40mm as shown:

window detail

Again, with hindsight, we should have used sightly deeper timber for the sub-frame (say 70-75mm) to account for the 10-15mm adhesive layer for the first insulation sheet. This would have saved a bit of  ‘shaving’ on the second layer, which, of course is a slight thermal compromise too.

The picture below shows the first layer of insulation running into the sub-frame.

window insulation

I believe the principle we have adopted is one of the best ways of minimising thermal bridges between the window frame and the surrounding masonry. We could have gone one step further and used a structural insulation material for the sub-frame, such as CompaCFoam, manufactured in Austria, but I was put off a bit by the costs (around 10x cost of timber), and, as we haven’t gone for ultra-high spec, thermal break window frames (£££), I didn’t think it was a worthwhile investment in this case (investment greater than energy saving). But, it’s worth a look.

Hope this helps and would be interested to hear if others have adopted a different approach.

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weeks 36 to 39: scaffolding comes down

Front of house

The big reveal…after an interminable wait for the scaffolding company, even to pick up the phone, they finally get them to come to take it down! But, it’s worth the wait. With the sweet chestnut cladding and steel Lindab gutters, the house looks great (completely unbiased opinion of course!). There is still a fair amount of finishing off to do: painting; render below DPC; roof profiles; sedum roof; etc., not to mention landscaping. Some of these works should be happening over the next couple of weeks.

Rear of house

The balcony is now usable. It is good and solid and almost thermal bridge free. The balustrade has been fitted: it looks okay, but not quite what we would have chosen (planning condition to match existing). Overall, though the rear of the house looks smart, and the rear extension, clad in the chestnut, smartly encloses the balcony at one end.

We haven’t quite decided on whether we should leave the chestnut to naturally silver, or whether we should lacquer it to retain the new-look colouring for as long as possible. The intention was to let it silver, but it’s nice as it is right now. I think we’re likely to leave it.

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weeks 36 to 39: ventilation installation

MVHR in Pantry

We are fitting a balanced mechanical ventilation system with a heat recovery unit (MVHR). This is a ducted supply and extract system that removes moist air from wet rooms and supplies fresh air to living rooms and bedrooms. The heat energy in the extract air stream is recovered by the heat recovery unit and this is channelled into the supply air stream so that the heat energy is not lost. I evaluate many of these systems as part of my work and have found that there are frequently problems with the way the systems are designed, installed, or commissioned.. Often there are shortcomings on all three elements, – and the systems are getting bad press as a result. As we are beginning to build to increasing airtightness standards (and we are going fairly airtight here), we need a ventilation strategy that will deliver fresh air to satisfy the need for good indoor air quality. But, it is important to mitigate the resultant energy losses (extracting heated air) and use (power for fan) by employing an efficient ventilation system. If it can recover heat energy, then all the better.

I am keen to evaluate a system that has been well-designed, installed and commissioned – to monitor the system over a period of years and get some really good long-term data on the performance of an efficiently operated system. We have opted for a Paul Novus 300 unit, which is currently one of the most efficient MVHR systems on the market (94.4% heat recovery efficiency) and is certified by the Passivhaus Institut. Whilst the system can be efficient, the weak link in many systems is the ductwork that links all the outlets to the MVHR system. As the photo shows, we are using Lindab SAFE ducting, which is tubular steel ducting – not flexible plastic that many systems are. I am a firm believer that the ducting should be considered part of the long term fabric of the property – the MVHR may need replacing after, say 20 years, but I would hope to connect to the existing ducts when the time comes and not rip the house apart to replace that. The resistance in a rigid ducting system is also much, much lower, compared to flexible, meaning the system will move air much more efficiently and quietly.

MVHR isometric design drawing

The installation, designed in association with the Green Building Store, has commenced on the lower ground floor, and will need to be done in two or three phases (so more posts to follow). The MVHR unit itself is going into the existing kitchen, but we can only install this once we have moved out and into the new kitchen.

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weeks 35 and 36: flooring

LGF flooring

The oak floor has now been installed on the lower ground floor. We use a local sanding specialist to both sand and oil the floor. At time of writing this post, the floor has only one coat of oil, but it looks really good. In the past I have hired floor sanders and got on with it myself, and was a bit sceptical on the advice that it should be done by a ‘professional’, but I was wrong. Knowing that the sanding company was doing the lower ground floor, I thought I would get them to do the hall on the ground floor too – a mixture of old flooring and new. The results were were astounding!

hall floor installation Hall sanding

First the hall floor was installed by the carpenters. We had the existing oak floor (made in early 1960s) re-profiled so that the extension in the hall matched. We were never sure how the old and new were going to blend in – until it was sanded…

old and new floor

The top half of the photo is the new floor, the bottom part of the photo is the existing floor – I thought it would look different, a little darker, but it is pretty much identical. It needs to be oiled next – that will be the acid test, I guess. I think I might get these guys to do the other floor boards in the house!


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