Changing Aux Switch Wiring on a Honeywell Zone Valve

The post is partly as a reminder to myself, and partly for anyone else who finds themselves with the same requirement.

On the boiler primary circuit for my new solar cylinder there’s a Honeywell V4043 2-port zone valve. This particular model is a H1056 which has 22mm compression fittings and a SPST (single pole, single throw) auxiliary switch. I need this switch to control the DHW suppression on my Viessmann Vitodens 100 boiler (I’ll elaborate on that another day), but the circuit has to be active when the 2-port is closed whereas the zone valve only has a wires for the common (C) and normally open (N/O) poles on the switch.

 

The New Boiler’s on order…

This is just a quick post to mention that I’ve now ordered a new gas boiler and solar hot water cylinder, ready for the renewal of my central heating system this summer.

Boiler sizing turned out to be a bit tricky. My current boiler, installed by the house’s previous owners in about 2001, is a Potterton Osprey CL150 which has a rated output of 44kW (yes, 44 – there I’ve said it!). As I might have mentioned previously, it always made an impressive ‘whumph’ when firing but last winter, despite us living in pretty cold conditions (e.g. ice on the insides of some of the windows) we still had a gas bill heading towards £1000.

So I’ve done a room-by-room heat loss calculation, followed by some whole house estimates (EST and SEDBUK) as a cross-check. The really difficult figure is determining the U-value for my 18″/450mm solid stone walls (limestone with rubble core). Estimates vary wildly from 1.05 to 2.13 so I’ve ended up taking the average of 1.6W/m2K – I suspect soft Dorset limestone is at the higher end of this range really. By my calculations, with the insulation as it is now, I need 23kW peak and, with the improved loft and some upstairs internal wall insulation planned for this summer, this falls to 19kW. This is based on an estimate of 3900W for ventilation losses (by volume) and 2000W for hot water. As a final sanity check I looked at our gas consumption last winter (~27,000 kWh over 6 months) and the 6 hours per day the boiler was running, and it conveniently came out at 25kW average.

My short-listed manufacturers were:

• Worcester-Bosch
• Vaillant
• Viessmann
• Broag-Remeha

As you might guess, I’m keen to install reasonably sophisticated controls to maximise the amount the boiler is condensing, as well as to be able to control which rooms are heated, to what temperature and when.

After much deliberation I’ve bought the lowest output Viessmann Vitodens 100-W (WB1B) system boiler which is rated at 26kW.  As an aside, the staff on the Viessmann technical support line are very helpful. This is still rather lower than the current 44kW rating but I’ve convinced my plumber that I’m happy to risk a smaller size on the basis that:

 

Solar Thermal: Permitted Development Notes

This summer my central heating replacement is definitely happening. At some point in the future I want to include solar thermal hot water heating so, given that I’ll be replacing my hot water cylinder anyway, this means I’ll need to fit one with twin coils (one for the boiler primary, the other for the solar circuit). Anyway, that is a topic for discussion another day.

Firstly, I thought I’d better find out what the planning situation for a solar collector was. The planning law changed a couple of years ago so that for most houses common renewable energy sources are covered by “permitted development” laws – in the same way that you are entitled in principle to build an extension of a certain size, you are now allowed to add solar thermal panels and solar PV – see the EST website and Planning Policy Statement 22.

The exceptions to this are Listed Buildings and buildings in a Conservation Area – the former always needs planning permission (I think) and the latter may need permission.

 

“Degree Days” – the effect of weather on energy usage

Carbon Trust: Degree Days Tool

Here’s a guest article from a friend of mine: enjoy!

“…all other things being equal, colder outside means more gas burnt inside to keep us warm. But how to disaggregate weather effects from energy efficiency measures and lifestyle changes? The key is the ‘degree day’ concept”…

I thought I’d let you and your readers know about my investigations into measuring the energy efficiency of my light-green old house, a late Victorian semi. It was prompted when EdF started sending me gas and electric bills comparing the most recent quarter with that of a year ago (see http://www.edfenergy.com/edf-energy/showPage.do?name=homeenergy.payingBill.understanding.gas.bill.til). It’s easy to be sceptical about how valuable such information is, so that’s what I was, but wanted to find out what suppliers could tell consumers that would be of use.

 

Traditional Radiators vs Underfloor Heating

Over the last year or two I’ve been pondering the replacement of my gas boiler and possibly quite a lot of the heating system (regular readers may remember that my heating pipes all drop down from the loft).

I’m on mains gas so have only considered gas condensing boilers, not more exotic technologies such as ground source heat pumps or wood pellet burners.

One of the key features of condensing boilers is the need to keep the return temperature down as low as possible – certainly below the dew point (55C), but some manufacturers also quote outputs at 30C (flow 40C) where the boilers appear to operate even more efficiently

 

PassivHaus standards

Recently I’ve been hearing more mentions of the German “PassivHaus” standard for energy-efficient houses, so I thought I’d look it up.

I found a UK website at www.passivhaus.org.uk sponsored by BRE and EST. Here they outline the PassivHaus standards – overall they say “the total energy demand for space heating and cooling is less than 15 kWh/m²/yr treated floor area” so for a 200m² house that is only 3000kWh pa for heating. They achieve this by strict specifications including the following:

• “All components of the exterior shell of a PassivHaus are insulated to achieve a U-Value that does not exceed 0.15 W/m²/K”
• “Windows (glazing and frames, combined) should have U-Values not exceeding 0.80 W/m²/K, with solar heat-gain coefficients around 50%”
• “Air leakage through unsealed joints must be less than 0.6 times the house volume per hour (this is the equivalent of an air permeability value of less than 1 m³/hr/m @ 50 Pa)”

Note they also discuss passive solar gain but with a renovation project you haven’t much scope to change window sizes and building orientation so I’ll ignore those aspects!

These are challenging requirements, so to what degree can we incorporate these ideals within an old house refurbishment?

 

Improved efficiency halogen lamps – continued

Following on from my post last year about Philips’ new higher efficiency halogen lamps I see that Osram have launched a whole new “energy saving” range too (see their website). This covers a wide range of filament lamps, curiously including a regular old-fashioned bayonet cap bulb!

 

New Year’s list

Well, here’s my list of house jobs for 2008 (or so!):

 

Installation of Loft Insulation – first instalment

The insulation in my loft has been sadly lacking: it probably started off at 2″ installed in the 60’s but these days, with the amount of dirt that comes through the (un-felted) roof, along with other compression over the years, it is rather thinner in many places.

I have done heat loss calculations to try and work out how to prioritise my efforts. For example the front bedroom has a total loss of 1500W (not including ventilation losses) at a temperature difference of 25 degrees. Of this I reckon 710W is lost through the outside walls, 370W through the windows and 450W through the ceiling – so about third is going through the loft (arguably a greater proportion when the heavy curtains are drawn). So, as you’d expect, the loft is a good candidate for improvement.

I have decided to use a combination of a reflective vapour control foil, rockwool and finally a layer of Celotex PIR thermal insulation board, which should reduce the U-value from around 1.0 down to ~0.15.

 

A pilot light surprise…

Just out of curiosity I measured the gas used by the pilot light on my 7 year old boiler.

This was measured on a coldish September day over a 12h period and turned out to be … 7kWh per day! This surprised me rather (it is equivalent to a good chunk of the electricity I use) so I tried again a few days later – the same result. So it’s either using that or I’ve got a leak so I tried switching off the boiler overnight and found that, fortunately, no gas was used.

OK, looking at this another way, is 7kWh per day a realistic number?