Saturday, 24 November 2012

First Year Data Graphs: Feedback welcome

It's icy this morning - have a look at the beautiful ice patterns on the roof windows before I bombard you with a year's worth of graphs...

Pretty isn't it and it shows quite clearly that we are warmer inside than out and not leaking heat through the triple-glazing.

OK, never mind the aesthetics, here's the info:

This shows the amount of energy we've used and how much we've generated using the PV panels and solar thermal tubes. It covers the period from the early September when it first became possible to measure the tube output.

Between May and the middle of October the energy usage for two people working (more-or-less) full time in the house was running at  just about 18 kWh a day. When the house is empty (but still has fridges etc. and the MVHR running at its lowest setting) the average is 11 kWh.

The red spike shows all this changing in the second part of October when the house got cold. When the internal temperature dropped below 18°C we started using extra heating. Initially we were just switching on a couple of plug-in radiators we'd bought in the two downstairs rooms and that accounts for the rise in energy use at the end of October. The next spike shows us turning on the top-up house heating. The MVHR has a unit that provides top-up heat but if you look at red line you'll see just how much energy it uses when it's on. We are currently running this just in the mornings to heat the whole house and then using the radiators as before for the evenings.

This next graph shows the data for all the past year and illustrates the impact of having the house's top-up heating on. It may be that we have got some of the settings wrong on the MVHR control panel but at the moment the house's own heating cannot heat the ground floor above 18 degrees even when the top-up heating is burning up the kWh so I'd welcome any twitter feedback as to why this is.

In the chart here you'll see that there is a difference between energy usage now and a year ago. We'd hoped that there would be a difference in the amount we needed to heat the house after a year of occupancy but the house is as cold this winter as it was a year ago. The only difference in energy use now is that last year we were trying to maintain the temperature on the ground floor at 20 degrees so the thermostat was set to that and we were running the house heating for longer. This year, at the moment, we're only heating the rooms we're in and keeping the doors closed to all the rooms. This is saving energy but it doesn't tally with all those cosy images of a passivhaus; I find myself yearning for coal fires and feeling warm. On sunny days the house is OK whilst the sun shines through the big windows but this part of the country doesn't get many sunny days so such treats are rare.

Another thing I wouldn't mind feedback on is the impact of windy days on the house - we've had airtight test showing the house isn't leaky, indeed at one stage this was the least leaky house in England(!) but wind definitely has a measurable cooling effect. It's like it drags the warm air out through the vents before the MVHR  has had a chance to reclaim the full amount of heat - is that possible twitter? Does anyone else have experience of this?

This graph shows the profile of the year with the purple arc of the external temperatures and the year's worth of sunshine. You can see how the three floors had a different temperature for most of the year until the autumn equinox. Does this mean the house has now reached equilibrium you may ask? Nope, it just shows me shutting all the doors on any but the sunniest days in an attempt to stop the heat inside the rooms from shooting up to the top floor. This graph also shows quite clearly that in summer we struggle to cool the house and in the winter we have trouble getting it above 18 degrees on the ground floor.

The final graph shows the electricity generation from the PV and solar as a percentage of our usage, despite the best efforts of the English weather.

If anyone would like the spreadsheet with the breakdown of all the readings then tweet me - there are several sheets but we're happy to share them with anyone who's interested.

Sunday, 11 November 2012

Annual Review

We've now been in the house for a year so this seems as good as time as any to give the house and its technology a check-up, so let's start outside the front door and work up to the roof.

The Insulation

The external insulation is a winner (mind you, I don't know how it might compare with cavity wall insulation).  Although this year the cold weather has arrived a month earlier we didn't need to put in additional heating until the outside temperature fell to about 8°C at the end of October. It's hard to judge how soon we would have put heating on in a 'normal' house but I should think this was a good month later and in the spring we turned the heating off in early March. It therefore looks like we only need heating for five months of the year (maybe!). 

The Porch
The porch is great on sunny days in spring and autumn as it traps the sun. You can then open the internal door and let the warmth into the entrance hall which reduces the amount of extra heating you need. In winter, especially on a grey day, it gets freezing and you have to be really quick coming through the door so the cold doesn't get into the hall. In summer you have to have all the windows and external door wide open in an (often unsuccessful) attempt to cool it down. Leave any plants in the porch between June and August and they fry but the rest of the time they flourish and I have spectacular cyclamen in winter. Basically, the porch is a very expensive greenhouse.

Maybe it's me but the word passive doesn't quite tally with our experience of the heating, cooling and ventilating of this house. In the summer we were forever trying to cool it down and now the weather is cold we have tried endless permutations to get the internal temperature comfortable.

Of all the aspects of the house that we've found vexing this is is the pièce de résistance!

In the summer we eventually evolved a convoluted system of  excluding the sunshine during the day, messing round with the MVHR and opening the windows on the top floor to draw heat up through the house but it was really only the dismal weather that made things tolerable. In summer the average internal temperature was about 23°C but it could reach 26° if we weren't careful.
Now the house is struggling maintaining 19° but to achieve this we've had to develop a system of turning the fans to their lowest setting when the heating system that comes with the MVHR is off and onto their middle setting when it's on. The electric heating uses the most phenomenal amount of energy so at the moment we have it on for five hours in the morning and in the evenings we have plug in radiators to warm the room we're in.

We're also having to remember that whilst in summer you keep all the doors and windows open, in winter you have to keep everything closed - except when the sun is shining because then you need to open all the doors and blinds to let the whole house warm up..... If you watch Dr Who you'll be aware of the running joke that the TARDIS has a mind of its own. We haven't had to resort to hitting the heating controls with a hammer but we've felt tempted on occasions.
So, on the space theme, here's Saturn again representing the vents that blast air, at various speeds, into the rooms from the fans. I know the physics of all this but I do wonder why they are placed where they are in the rooms. The only room where you really feel the benefit of the system is the room where the desk is directly opposite the vent so I'm not sure why we don't have under-floor heating of some kind instead but maybe that's my inner classicist coming out. In the same way, in the summer, it was only sitting at the desk that you could feel the benefit of cool air coming in from the fans.

The corridors don't have vents at all so in winter, unless you keep the doors open, the corridors get very cold and in summer, as I've mentioned before, there seems to be no way (apart from opening the windows) of cooling the top floor so, in general, I remain baffled by the MVHR system (even with an English version of the manual).

Hot Water
I promised you a picture of the new 'improved' hot water cylinder back in September and here it is.

Looking back I see the spec for the water cylinder that preceded this one; as far as we can tell changing the cylinder hasn't made any difference to its efficiency.

The only difference we've noticed is that the display now works.
This means that we can now quantify how much energy the solar tubes produce, as the generation meter only records the PV generation. By the power of mathematics this has allowed us to calculate that over the year we pretty much generate 100% of the energy we use, even taking into account the poor summer and chilly autumn.
Chuck a few sunny autumn and winter days into the mix and we will be generating more than 100% of our energy over a year. The graphs will appear in a later post. 

Rainwater Harvester 
Oh dear.

Well, it's been drained and cleaned and had its pump replaced but the only time we've used it is when the local water board turned off the water supply for a day.

It works for the loos on the ground floor and it works on the middle floor but, alas, whilst the pump can pump the water from the harvester up into the house it can't pump it up to the top floor so it's only 50% effective.

Also, since the pump was replaced, everytime you flush a loo there is a curious rumbling sound like a distant pneumatic drill. Not that that is so much of a problem in the winter because you're having to keep all the doors closed (see above).

Really easy to clean and great cooling effect in summer but equally cool in winter so you need to wear sheepskin slippers to keep warm.

Drop something on it and it shatters neatly - there is no bounce at all so I'm glad there are no toddlers in the house.
In order to be more eco we have reduced water flow and this is another thing that drives me mad. It means that it take four minutes (believe me, I've timed it I was so incredulous) for the shower to run warm water if you're having the first shower of the day and four minutes to start hot water coming out of the tap when you wash up. Ironically it means you run the taps longer than you would just so you can get hot water, go figure.
External Blinds & Triple Glazing
The blinds play a vital role in keeping the house cool but in a perfect world we would have them on the east window on the first floor and the long windows on the west as both let heat in in summer. We also badly need external blinds on all the roof windows - including the ones on the north side of the house, especially at the western end as in summer the sun is high enough in the sky to shine directly in. The triple glazing is brilliant and there's no noticeable loss of heat through it so whether you sit next to the window or on the other side of the room the temperature feels the same.

PV Panels

28 panels and they generate enough energy to run a home and an office, including all our heating. Plus the house is occupied 24/7 and we're not hair-shirted greens we do have DAB radios (6 Music is the only thing that keeps me sane!), TV, laptops etc.

Does someone want to explain to me why we don't have a Green New Deal to put solar panels on all public buildings?