Coed Cae B&B, Taicynhaeaf, Dolgellau, Gwynedd, Wales, LL40 2TU
01341 430628 / 07909 996983 or e-mail: info@coedcae.co.uk
Bed and Breakfast accommodation in the Snowdonia National Park

Spring 2008
I have become a bore!
There are some who would say that there is nothing new here, and that the desire to share understanding beyond what others may consider ...err... interesting has long been evident. A key difference is that now I can see it in myself. I have become a bore.

In particular a heating bore. Well not so much heating, as the peculiarities of trying to marry thermal storage technology to solar heating circuitry whilst maintaining ...and there I go again.
We have been on a journey with our heating system; one that changed us irrevocably. It was a journey from ignorance to understanding, from naivety to enlightenment, from cold to warm, from fear of plumbing to being able to draw a heating circuit for the whole system. In short, from normal to boring. Like I said.

There were no two ways about it, this was to be an expensive venture. As well as the heating hardware, we needed to build a boiler house to enclose it, and a series of dry log stores for the fuel. Fortunately at the time, various streams of funding were available to help with the installation of carbon-neutral technology. We had been working on the principle of installing a system to which we could add solar water heating at a later date, but in the end bundled the lot together on the application. The form filling for a business application was quite a task, it being the same form as a health trust would fill in to convert their hospitals, and we failed on our first attempt. Given that you are only permitted two application attempts this was a blow, but we addressed the problems, reapplied and were successful. The grant only applied to the specific technology (i.e. the boiler and panels, but not the boiler house or the plumbing required to attach to an existing heating circuit) and covered about half of the cost.

One of the stipulations of the grant was that installation be carried out by an accredited engineer, and by chance we noticed that one of them The Green Heat Team was based about 4 miles up the road in Dolgellau. We were aware that they were a fairly new business with only a few installations under their belt, but mindful of the leaps of faith given to us over the years and the potential benefits of dealing with a local firm, we decided to go with them. We had scheduled the installation for late autumn, it being a quiet time for the B&B, and the switch from Rayburn to log boiler occurred just before Christmas. On commissioning the new system, it was immediately obvious that things were not going as planned.

The lack of background experience of the Green heat team had been a concern, but turned out to be a red herring; the technology itself, or the way we were using it, was sufficiently new that when we ran into problems even the importers of the hardware were floundering and giving different answers each time we spoke. In the end, most technical problems were ironed out around the kitchen table with ourselves, Andy from GHT and large piles of scrap paper. In order to make any kind of valid contribution to the discussion we had to get up to speed on conventional heating systems, then bin much of what we had learned as we got to grips with the new technology. I think that it was around this point we became boring.

Christmas was spent with clip-board and/or thermometer in hand checking various parameters, or trying to explain the system to anyone prepared to listen (in itself a dwindling supply). Because we were effectively making it up as we went along, it took time changing settings and logging the effects on the system. Slowly but surely we ironed out the problems, redesigning bits along the way when required until the system was fully active. Not withstanding the pressure of needing the place heated for B&B guests whilst working around an unfamiliar system, the whole process of design, installation and troubleshooting has been strangely satisfying, and to be honest, I think we ended up with a better system than we initially specified. To a large part that would be because the original design didn’t work, but if it had worked, what we ended up with is better.

Details of the system itself, problems experienced along the way, and various redesigns are detailed below lest you become as nerdy as us!

The heating system was designed around thermal store technology. In this set-up a huge insulated Akvaterm accumulator tank  containing 1500 litres of water acts as a heat store that can be added to or drawn upon, much like a rechargeable battery.

Heat In
Heat can be added to the store in a number of different ways, depending on the technology chosen. In our system the primary heat source is an Atmos 18 log boiler. The boiler is connected to the accumulator tank by a Laddomat 21 unit; a sophisticated set of valves designed to charge the accumulator tank to its full temperature while saving the boiler. In operation it creates an expanding layer of hot water at the top of the tank, and the production and maintenance of such stratification is key to efficient use of thermal store technology. The manufacturers have a rather nifty PowerPoint presentation which explains the process in more detail.
We had originally planned to run a solar heating circuit (via a heat exchange coil) through the colder strata at the bottom of the accumulator tank to help during the summer months.

Heat Out
Domestic hot water (i.e for the hot taps, DHW) is drawn from a mains-feed and is heated to temperature by being passed through a heat exchange coil in the hot strata at the top of the tank. Water for the radiators is drawn directly from the tank and mixed to the required temperature using return water via a ThermOmatic K constant heat regulator.

So far so good. Or not, as the case may be.

1. Whilst firing the boiler the tank stratified as expected with hot at the top and cold at the bottom, but the minute the heating switched on the whole tank got mixed up, so instead of half a tank at 70 oC (useable temperate) we ended up with a full tank at 35 oC (unuseable). As a result we ended up with no heating and no DHW.
2. The change to a pressured DHW system meant that the temperature regulator valve in our shower no longer worked, and some of the joints in the existing pipework started leaking.
3. The solar circuitry only activates when the panel temperature (on the roof) is higher than the coil temperature (at the bottom of the tank) The de-stratification of the tank meant that the bottom of the tank was warm, which in turn meant that the solar panels were never likely to operate.

When the stratification was breaking down, there seemed very little help to be found from the equipment suppliers. A particular low point (both for us and the GHT) was when we hit the answer “well, storage technology doesn’t really work that well on radiator systems, it is much better for under-floor heating which work at a lower temperature”. Great! Nobody was putting that in their adverts! Anyway, at this point, with no intention of re-plumbing the entire house and with a strong stubborn streak, we set about MAKING it work.

But first I need to acquaint you with the heating circuit plumbing into the storage tank. The hot water is drawn from the top and returns to the bottom. In an ideal world where stratification is maintained, hot water is drawn off at the top, loses its heat in the house, and returns cold to the bottom. If warm water is returned to the bottom of the tank, it messes things up pretty quickly. We figured that the hot water needed as much an opportunity to lose its heat as possible, and the longer it was in the heating circuit, the more heat loss would occur. With this in mind we set the circulation pump on its slowest setting and it instantly improved things. However, the heat loss ultimately depends on the demands being placed on it by the system, and if most of the radiators are turned off, the water may still return hot. There is a further feature to the plumbing; the outflow and return pipes are bridged by a shunt so that the pipework resembles a letter H turned on its side. The shunt is controlled by a ThermOmatic K valve which redirects hot return water through the shunt and back around the heating circuit rather than allowing it into the bottom of the tank. This again minimises the disturbance to the tank strata.

There was a whole set of issues relating to this valve, mainly associated with where to place the temperature probe. The received wisdom was to have the probe stabilising the outflow temperature. We batted this one around until our heads hurt, and, no longer placing much value on received wisdom, tried various positions and settings. We currently have it on the return pipe, set at 55 oC, so if the water returns above that temp, it gets sent around the system again. The idea behind this is that when the hotter water is used up, the whole tank still contains serviceable domestic hot water (DHW), which is important to our B&B guests. However, this still left a lot of warm water at the bottom of the tank. To make better use of this, and to further stabilize the stratification, the DHW was re-routed through a heat-exchange coil at the bottom of the tank before it passed through the normal coil at the top. In this way the cold mains-feed water was preheated by the cooler water at the bottom of the tank then topped up by the hot water at the top. This constantly works to re-establish the stratification by taking heat primarily from the bottom of the tank.

Because the solar was getting little opportunity to contribute to the accumulator tank, we decided to change tack and use it to further pre-heat the DHW. This meant a separate dedicated tank (250 litre, I think) for the solar heating. The DHW was sent through a heat exchange at the top of the solar tank before heading off to the accumulator tank. By being first in the pre-heat sequence, and therefore exposed to cold water every time a hot tap is turned on, the heat in the solar tank is quickly removed, and thus the tank is kept relatively cool. This means that the panels have to heat up less before the system is activated, and so even on fairly overcast winter’s days the panels are contributing.
The system as described is fine for when the heating is running (Winter), but we needed to anticipate other situations. For example on hot summers days the solar system may be producing enough hot water on its own, and we would not want the water to be cooled by passing through a cold accumulator tank (a situation termed “Summer A”). Equally, if during the summer months, we fired the boiler to top up the hot water, we would not want the solar water being cooled by the bottom of the tank (“Summer B”). These needs led to much head-scratching and we couldn’t come up with an effective way of automating the three useful permutations: solar only, solar plus top of the accumulator, solar plus bottom and top of accumulator. In the end we put in mechanical valves and will have to manage this ourselves.