Turboburn Monitor

Turboburn heat exchange coils

Living as I do in a Christian community our "home" is large. Its ancient construction makes it a very inefficient building for heating and our past electricity and fuel oil bills have been horrendous. Enter Frank Murhill who manufactures the Turboburn range of wood-burning boilers in Ireland for the European market. I had been looking for some time for a solid-fuel alternative and liked the idea of a heat accumulator, but had been put off by complex controls, complex terminology and convoluted flue passages with implied cleaning difficulties. And then there was the choice of wood chip, pellet or logs. When I was shown a Turboburn flier I was pretty sure it was the answer to my quest.  It took a year or so to finalise our decision and several more months to install our Turboburn TB4, the TB4 being the largest model that Frank sells.

Turboburn inners - from their website

The purpose of this post is partly to give a testimonial of how Turboburn met our heating requirements and partly to point out what we had to contribute to make the system work the way we wanted.  I figure that our experiences may help the next person who chooses to install this kind of system.

Here are some links to some smart-phone videos Frank has taken of our system:
Video#1,  Video#2,  Video#3

First a brief explanation of how the Turboburn works.

The Turboburn is basically a huge tank or "bath" of stagnant water completely surrounding a fan-driven firebox connected via "fire tubes" to a smokebox and flue - rather like a steam locomotive. Coiled copper-pipe heat-exchangers towards the top of the tank deliver hot water to taps or central heating as required.

Frank says that having the firebox totally surrounded and thus cooled by water makes it virtually impervious to being destroyed by heat. The fan makes the fire burn at a high temperature and thus very efficiently and with little ash and no build-up of pitch in the flue.  We fire our TB4 boiler once per day and let it burn out after 2 to 6 hours. The idea is to raise the temperature of the water bath to as near to boiling point as is practicable and thus to store enough heat to last until the same time the following day.

For example, at the moment it is 9pm and I last topped the boiler up an hour or so ago. The water temperature is now at 97 degrees C and the fan has just turned off. It may rise another degree but by experience I know it is unlikely to reach boiling point. This is just how I want it - plenty of spare heat to last through tomorrow until stoking time which, for us, is usually around 4pm.

Our monitoring software

We turn off our heating demand at night - the hot water cylinders store enough hot water for washing. The graph above shows just how good the TB4 insulation is - just a couple of degrees drop over 4 hours. And then the sudden plummet when the heating comes on at 06:30 a.m.  More about our monitoring software in my next TB4 post.

If demand is low, as it would be in the summer, we are told it will suffice to stoke every other day.

The beauty of the boiler is its simplicity. Provided ash is occasionally cleaned out (we do this once every couple of weeks) there is nothing to go wrong. The water bath is vented to the atmosphere so, whilst undesirable, boiling is entirely safe. Corrosion inhibitor prevents rusting which an open tank would otherwise suffer from.

We used to spend thousands a year on fuel oil and had three 3kW electric immersion heaters running 24/7. Since the Turboburn was installed we have not used the immersions or oil boiler at all.

We installed our TB4 boiler on a concrete pad some 40m away from the house and have subsequently built a shed around it. We have made a wood-processing yard surrounding this shed.

Because of the geometry of our buildings we have two separate central heating circuits and two separate hot water systems.

Having multiple heat exchangers made is easy to connect these up with minimal changes apart from the obvious underground link from the house to the boiler.

Even though the cost of wood is significantly less than that of oil or electricity, this type of boiler will not suit everyone. We have had three truck loads of timber in eight foot lengths delivered so far. That's a lot of wood. The first task is to chain-saw into rounds about 2ft long. Larger rounds have to be split. The timber then has to be stacked to dry for as long as possible - we plan to have about a year's supply of wood drying. All this takes a fair bit of hard labour and a fair bit of space.

Other fuels are possible - before making the purchase we visited a Turboburn owner who grows elephant grass as fuel. And it is possible to fit an oil burner though I cannot imagine why anyone would so that.

We told Frank that we wanted him to supply the boiler but we would do all other installation work ourselves. And this is exactly what happened.  We laid the concrete slab for the boiler, Frank placed the boiler onto this slab, added insulation, cladding and flue (chimney), supervised the filling of the tank and did a test burn. We erected the shed around the boiler and did all the plumbing and electrical hook-up. Since then Frank has made several return visits to make sure everything is running correctly, and has lent us a hydraulic log splitter.

Frank's log splitter in action

For boiler control, Frank supplied and fitted the fan and then simply handed over a 2 hour timer switch and a thermostatic trip switch for me to fit. He gave advice on how to lay the underground pipes, but we did this work. So here's a list of what we did:-

• We hired a digger to cut trenches 1m deep for our pipes, one trench for each of our two central heating systems. The longer trench was about 60m in length.

The shorter trench to the main house

The longer trench meanders to avoid an ESB duct

• We insulated and then laid our feed and return pipes in the shorter trench to the main house:

Three circuits in 3/4" pex for heating each pipe insulated with19mm thick Armaflex.

One circuit in 3/4" for direct hot-water each pipe insulated with19mm thick Armaflex.

These insulated pipes wrapped in builder's polythene

One 4" duct for future services laid on top

A manhole is needed to give access to joints
because pex pipe comes in 50m lengths and the trench
was over 60m long

• Likewise for the longer trench to the house extension:

Two circuits in 1" pex for heating each pipe insulated with19mm thick Armaflex.

One circuit in 3/4" for direct hot-water each pipe insulated with19mm thick Armaflex.

These insulated pipes wrapped in builder's polythene

One 4" duct for future services laid on top

Threading the insulation onto the pipe

• Each circuit terminates in its own heat-exchange-coil at the TB4 end, each with its 1" thermostatic mixer valve. The later is necessary because the TB4 temperature varies up to boiling point, whereas the heating water needs to be at around 70 degC and the hot-water around 55 degC. In any case pex pipe is not rated for much more than 80 degC.

• At the main house end, the three 3/4" circuits each have a 6m head circulating pump and NRV (non-return-valve) and then are connected in parallel and join the main house heating trunk circuit behind our existing oil-boiler (also with NRZ). We have retained the oil-boiler as a backup.

Three 3/4" circuits in parallel drive the existing
main house heating load

• At the main-house end, the 3/4" direct-hot-water feed connects via a bronze circulating pump  to the tops of our existing twin HWC (hot water cylinders), and the return is taken from the bottom. These HWC's serve four bathrooms and several other hand-basins. In operation the pump pushes water heated in the TB4 from top downwards into the HWC's. A thermostat near the bottom of one HWC turns the pump off when above about about 40 degC, at which point the tank is virtually full of hot water. A detail is that the feed flows via a 3-port valve into the HWC's - when the pump is first turned on the valve diverts water directly back to the return and thus avoids the trench-worth of water, which by this time may be cold, from entering the HWC's. After a timed delay of several minutes the valve is energised so that the water, which by this time will be hot, is fed into the HWC's.  This system provided endless hot water and its efficiency is evident in that the return pipe is usually cold or just warm - so that I have not needed to lag it where it runs above ground within the house.

• At the house extension end of the longer trench, the two 1" heating circuits will be connected in parallel in a manifold feeding various radiators pending renovation work. The 3/4" hot-water circuit will serve bathrooms in this extension to be as well as at present being connected to the third existing HWC which serves the main house kitchen.

• We prepared the boiler site and laid a 150mm thick, reinforced concrete slab

Here comes the boiler !

Frank unloading the boiler

Positioning on our slab

On goes the second chimney section

Various layers of insulation, about 9" in total

The first fire is lit

Now it is burning hot !

Part 2 deals with the electrical installation.
See also Turboburn Monitor Plus