Thursday, 14 November 2013

Two Years In: How Green Technology Works

Today we've been in this house for exactly two years so I'm finally getting round to a new post with a performance review of the house to date. I think the fact that I've not posted up till now indicates how much things have settled down, as establishing how the house works is no longer an issue.....
............................. THIS IS A GOOD THING!


I don't know if it's too early in the season to speculate but the house doesn't seem as chilly as a year ago and we're only needing to add a little extra heat at the moment. Why that is we're not entirely sure - my OH wonders whether the house structure has needed this long to warm up and I'm wondering if it's because I have sussed how to get the incoming air to switch from one external pipe or the other (more of this below). Either way we are more comfortable in the house - except when I do cleaning when the combination of trekking up and down all the stairs and the heat blasted out by the hoover adds considerably to heat gain!

Last winter we were advised to warm the house using the top-up heating attached to the MVHR pipe system. This certainly heats the air going round the house but we found that the structure of the house with its stairwell-chimney effect and consequent air movement meant that all the heated air rose to the top floor resulting in what we technically call the Goldilocks effect over the three floors. This winter we are going to try out a more topical system and heat the rooms we're working in, secure in the knowledge that the top floor will warm up anyway. 

With that in mind I have purchased at enormous expense one of these heaters. It's made by Dyson and costs about five times the cost of a normal plug-in radiator but its claims are big. Given the weird air movement in our sitting room I've splashed out with some of the FIT money on this to see if it works better than last year's efforts in the room. Last night I plugged it in for the first time and although I had to turn the TV volume up by one notch I only needed the heater on for literally ten minutes before the room temperature rose by 1 degree so that was quite impressive.

It's early days though, so watch this space and see if the Dyson claims are true and it's worth buying - unless they unexpectedly offer me vast sums of money(!) it will be an honest response.

The frosts started here last week so we've run the MVHR's top-up heating for a couple of hours first thing in the morning to take the chill off but other than that the only heating we've needed to get things comfortable have been the ten minute blast of heat into the sitting room and running a 1kw heater in the office. That's been enough to have the rooms at 21 degrees so we don't yet need to take the glib advice of millionaires and wear lots of jumpers.

One thing that does make a difference to the heat in the house is the number of people and electrical equipment that's running. Three people and three computers warm the house considerably more than two. I suppose this is obvious but I'm not sure you notice that in a 'normal' house. Even turning the TV on warms a room up after a while and dispenses with the need for extra heat so you're regularly thinking 'should I turn that off and save energy' or  'should I turn that on and save heating'. I suppose I could measure the pros and cons of both options, but I'm not that weird. One amusing thing is the impact of school parties coming to see the technology as 15 teenagers generate a massive amount of heat and warm the office nicely, I'm always reminded of those suits in Dune.

Solar Technology

We have two sorts of solar tech on our roof. The recognisable photovoltaic panels to generate our electricity and vacuum tubes to heat our hot water. We have always been able to measure the amount of energy the panels generate as we have to pass the readings to Good Energy but we've only been able to measure the effectiveness of the tubes for the past 15 months when the new hot water cylinder was installed.

As of today we've generated 2941 kWh for the hot water which is slightly under Ofgem's calculated average electricity consumption for a year. That's a pretty impressive figure for something that takes up a relatively small proportion of the roof.

It appears from our calculations that the vacuum tubes produce more energy per cm of roof compared to the PV panels but there is a caveat that whilst all the energy from the PV goes onto the grid, not all of the heat produced by the tubes is used for the hot water in the summer because above a certain temperature the excess heat is dumped outside. Apparently we should we using this by having a jacuzzi - yeah, right. I'm not sure, therefore, whether we wouldn't have been better off having extra PV panels on the roof rather than the tubes but I'd need to calculate that and I haven't got round to it yet. 

Either way we generated about 89% of our energy usage in the last twelve months and that included a winter when the sun hardly shone and the snow stayed for weeks.

There is a lot of talk dismissing solar technology at the moment as part of the anti-green agenda but, you know what, it works and if it can work in this neck of the woods where the sunny days are such a rare thing that locals write songs praising their glory then it can certainly work in areas that get more sun than this. Even in the grey West Midlands a quick calculation of the financial return on the investment in the solar tech on the roof suggests that it will have paid for itself within about seven years so think what you'd make with a roof in Suffolk or the Isle of Purbeck. This, of course, assumes that the solar industry continues to get government support to get going .....

The Ground Pipe Diverter

I talked a bit about this last time: on either side of the garden we have these air inlets for the house.


The one on the north side of the house, just a few centimetres from the wall, draws air into the house through a short underground pipe, so the incoming air is at the same temperature as the air outside.

The other inlet is in the far corner of the garden and draws the air into the house via over 80 metres of pipe so the air is heated or cooled to the temperature of the soil.
Inside the house the two incoming pipes join and I can use the control panel in the hallway to set the parameters for the 'ground pipe diverter'. This opens or closes a flap where the pipes meet and determines whether I have air coming into the MVHR at the same temperature as outside or pre-cooled/pre-warmed by the ground. In winter this means the air needs to be heated by the heat exchanger from a starting point of 8-12 degrees rather than much lower temperatures, thereby using less energy to get the air in the house up to our preferred temperature - clever eh?

And Finally... The Rant

Insidiously, the high cost of energy in this country appears to now be the fault of subsidies for the poor and the green movement rather than the profit-driven energy companies. I don't know if living in an eco house therefore makes us the new enemies within but I do know that if every house in the country had access to the sort of technology this one does then the country's energy bill and energy load on the planet would be considerably less. Of course less energy use means less profits for the energy industry so never mind the impact of climate change on places like the Philippines last week or the potential for the UK to develop cheaper green technology and get a more balanced economy. cui bono - or 'follow the money' as our US friends say.

I can't end with a negative: cheer yourselves up with the knowledge that it's not all doom and gloom by reading about some more enlightened housing developments in Oldham that featured in The Guardian a couple of weeks ago. We'll get there eventually!

Thursday, 11 July 2013

Living In Harmony with My House

It is very odd to live in a house with a personality (GoT and Harry Potter notwithstanding) but that's what we've got here. After 15 months of living with each other I finally realised the house was on our side when it trapped two strangers in the porch for nearly an hour and wouldn't let them out (not so much a case of beware of the dog, but beware of the house!). Since then I've been applying intuition and science to the process of working out how the house likes to be treated and, thanks to engineering friends and email correspondents, we're now getting along fine.

As ever we've had a regular supply of visitors to look at the technology, tweak things and mutter dark remarks about other visitors who have been out to look at the technology and tweak things. This used to get me down but since the house started to repel boarders I've found it more amusing and the more I understand the house, the better I become at asking the right questions and minimising the number of tweaking visitors - it's like a domesticated version of homeostasis really.

But enough rambling, you're reading for the success or otherwise of the project so let's get on to the science bit (© stupid adverts):

The Rainwater Harvester

We are still waiting for the rainwater harvester to deliver as the loos on the top floor cannot refill when flushed, unless they are supplied by mains water. About a month ago several gentlemen from the company that provided the harvester spent an afternoon in the house with buckets, lifted up the manhole covers in the garden and shook their heads at the folly of earlier gentlemen. It turns out that the water supply to the harvester should come into the house via a flexible pipe rather than a normal pipe network and it is the joints in the current arrangement that lead to the impressive water hammer whenever we switch from mains water to the harvester supply. On the plus side, whatever they did during their visit, stopped the sound of running water that we had been experiencing 24/7 since January and apparently once the solid pipe supply is replaced all will be well. They assure me that this work will not necessitate any digging up of my garden which is good news because the garden has undergone a transformation thanks to considerable effort by yours truly ...

... and if my artistic endeavours are damaged I will be forced to loose the house on them

Solar Gain

Last summer the top floor exceeded temperatures of 26 degrees on sunny days in summer due to a combination of the warm air in the house rising and the lack of shading which then allowed sunlight through the triple-glazed roof windows. We expected the south-facing rooms to heat up but we were surprised that between May and July the two windows on the north corridor also had sun pouring through them. Last month, just in the nick of time for the heatwave, we had canvas external blinds fitted and that has reduced the temperatures on the top floor by at least 3 degrees. The blinds only reduce the light in the rooms a little, as if it were a cloudy day, but the heat reduction is phenomenal.

Air Flow

In my last blog post I was puzzled by the fact that in winter the ground floor rooms were cold, despite both the amount of extra heat we were pumping into the building and the claims that this house would be a constant temperature throughout the year. During the snows of February/March, following a discussion during a school visit, my suspicions about the structure of the house were confirmed. Essentially our stairwell acts like a chimney and draws all the heat of the building up to the top of the house. The ventilation system pushes extremely warm air into the rooms through the little Saturn openings and this is supposed to obey the coanda effect and waft across the room gradually cooling and sinking as it goes and bathing everyone on the far side of the room in its warmth. Unfortunately, on the ground floor, the force of the draw through the 'chimney' of the a three-storey stairwell is stronger, so the warm air gets about half way across the room before being sucked out under the door and off to the top floor. This is great during a summer heatwave but by the end of the winter I was putting a plug-in radiator on the opposite side of the room to the door and benefitting from that warm air going over me on its journey roofwards.


The Mechanical Ventilation. Heat Recovery (MVHR) system is what stops us running out of air in our airtight house and as well as supplying constant fresh air it assumes that if the house is cold you want to warm this air up and if the house is too hot you want to cool it. Thus the air coming into the house might, or might not, be warmed by reclaiming the heat energy from the outgoing air. Sounds simple unless you get given the manual in German and instructions whilst you're unpacking crates a couple of days after moving. Anyway, after many a happy hour trying to make sense of this (thanks to Sue and John for the engineering help!) and following advice from Green Building Store, when I had my notebook ready, I now understand how this works. Depending on the parameters I set on the touch panel in my hallway I can tell the MVHR to reclaim the heat or not reclaim the heat and decide whether I want to draw in air at the same temperature as the outside air, or air that has been pre-cooled or warmed (depending on the season) by being passed under the ground in the rehau pipes. I did actually know the theory of all this before now but I couldn't find out how to do it and my new knowledge plus the external top floor blinds means the house is much more comfortable on a sunny day. If I need extra cooling I just have to calculate whether the external temperature is higher or lower than the internal and open the windows on the relevant floor if I want to 'purge the heat'. Once you get the hang of it it's all very simple and logical but there's nothing passive about all this is there? Although, of course, the word passive does come from the Latin verb patior which my dictionary suggests could be translated as 'to put up with something'.


When we first moved in I was rather sceptical about the addition of a hogitat to attract hedgehogs but our household has actually been supplemented by a hedgehog. Admittedly said hog isn't living in his/her recommended abode but in a corner of the garden I've left wild but it is the first hedgehog I've seen since we moved to this neck of the woods.

Similarly the new pond was alive with tadpoles and water boatmen this year who all found their way to it unaided.

We have also done our bit for bees by having lots of nectar-rich plants and planting grass seed that has turned out to be predominantly clover. This will be all well and good for enriching the soil by fixing nitrogen but the bees adore it so grass cutting now includes shooing bees and froglets out of the way of the mower. It makes mowing rather complicated but as this is the only planet we've got I figure it's worth looking after!

Wednesday, 6 February 2013

Where Is the Heat Going?

We're now six weeks after the winter solstice and the PV panels have started generating electricity again on sunny days. The solar thermal tubes have been sunk into gloom for weeks and refusing to heat more than the odd drop of water so presumably they are more prone to SAD than the panels. They also have less surface area too of course, which probably is a more accurate explanation for their inactivity.

This latest graph represents the data for the past year and shows that the house is repeating its bad habits of a year ago in its consumption of energy. The crimson line on the right side is just depicting the heat energy we are having to add. As the temperatures dropped outside in the autumn the house cooled and we started to add extra heat. This heating made no discernible difference to temperatures on the bottom floor, which continued to fall, but it did push temperatures up on the top floor and made the bedrooms over-warm.

If you are an engineer this may all make sense but I find myself baffled as to what is going on here. My understanding is that, basically, this house is a sealed box and we've seen the air pressure tests to show that it doesn't leak. The only way air gets in or out, when the windows are closed, is either by opening the front door or through the pipes going to and from the MVHR. So, dear reader, where is all this heat energy going? Some of it is clearly bouncing around at the top of the bedroom ceilings but, where is the rest of it? The MVHR is supposed to recover "up to 99%" of the heat in the pipes before it vents the stale air outside the building but, for the life of me, I don't know where it's hiding.

All I do know is that, at the moment, we are pumping extra heat into the house but the ground floor rooms are no warmer than a year ago. As Kermit the Frog sagely remarked, "it's not that easy being green".