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First Month of Central Heating

by Unknown - 13:50 on 27 October 2013

On 2nd. October, we completed our first (lunar = 28 days) month of using our Klover Smart 120 for central heating. We had used it in the summer months for cooking and hot water, but it hardly seemed worth reporting anything until we had tried the central heating. As well as central heating, the Smart provides a lot of direct space-heating to the surrounding air in the kitchen and dining room. During this first month we ran the Smart 120 at a maximum output setting of 3, which corresponds to the minimum level which Klover recommend for cooking. We ran it from 6.20-10 in the morning and 4.20-10.30 in the evening. The house stayed warm in between the two heating periods.

We are very pleased with the Smart's performance. A qualitative overview is that our house has been much warmer than it has been in previous years when we used a combination of oil and wood stoves and we think that the cost of this warmth has been affordable. Admittedly part of the reason for the house being warmer is that we would not normally have turned our central heating on quite so early in September because of the cost of oil. The oil boiler would only have been programmed to be on a couple of hours a day for hot water. On the other hand,we would undoubtedly have used our wood stoves quite often whereas with the Klover on we did not use them at all. A caveat is that this first month was mild. Indeed, occasionally the house was  a little hotter than we needed,but we  kept the system on even so for cooking. Consequently we saved the gas we would otherwise have used for our hob and electricity for the oven(although on electricity see my comment below).

I have kept a spreadsheet giving the weight of the pellets used in the Smart. We have a large bulk hopper so we can buy pellets economically, but we do not have an automatic auger feed to the Smart. I carry floppy buckets fromthe outhouse where the bulk hopper is to the Smart. I use a spring balance to weigh the pellets so my measure of weigh is rough and ready. Also, we have had a meter installed so that we can measure the Smart's input in kilowatt hours into the central heating/hot water system. Klover give manufacturer's figures for the division of heat between output to the central heating/hot water and output to direct space heating into the space around the Smart. According to Klover's figures, the division between space heating and central heating output varies as its output level varies. They give figures for its maximum output of 17.5 kilowatts to water and 5.2 kilowatts to space, thus for every 1 kilowat tto water about .297 goes to direct space heating. But the figures they give for its minimum output level of 1 are 4.5 kilowatts to water and 2.4 kilowatts todirect space heating, thus for every 1 kilowatt to water about .533 kilowattsgoes to direct space heating. They do not give figures for its medium output(level 3), so I have taken the average between maximum and minimum, thus I have assumed that for every 1 kilowatt to water, there will be about .412 kilowattsto direct space heating. I have used this ratio to calculate the overall heatoutput of the Smart and thereby to calculate an imputed efficiency for it. Whether this imputed efficiency is the real efficiency is very questionable,rather it gives us a lower bound for estimating its efficiency. Reasons fortreating it as a lower bound are:

1. Klover's figures for output are steady state figures measured after the Klover has heated up to working temperature, but in reality heat is used to heat up the Klover before it gets to a full working temperature and then, for some hours after the Klover is switched off, this heat is dissipated into the room. This heat is considerable. The Klover functions as a kind of storage radiator after it is turned off. Because of this, the proportion of output to space heating is, I believe, higher than Klover's figures.
2. Our installer, Greenflame Installations, acting on the advice of Firepower Heating (part of the same group as Stovesonline), installed an ESBE valve in the system. This enables the Smart 120 to heat up faster than it otherwise would. In a low temperature range (standardly up to 60 degrees), the valve diverts water back to the Smart instead of allowing it to circulate in the central heating/hot water system. In a further range (standardly 60-70 degrees) it gradually opens. Thus it is only above a certain temperature (standardly 70 degrees) that the valve allows a full flow of hot water to circulate through the central heating/hot water circuits). We have the Smart's target hot water temperature set at 74 (the default is 70). It progressively reduces its output as it approaches the target, thus 5 up to 70, 4 up 71, 3 up to 72, 2 up to 73, 1 at 74 (in actuality in the first month we had it set at a maximum of 3, thus it maintained 3 until it reached 72). In our house, the Smart spends a lot of its time with its water temperature below 70 (see 3 below), so I think that most of the time it does not give its designed output to the central heating system but gives more than its design output to space heating.
3. In our house, we have a special programmer which controls two heating circuits as well as a hot water circuit. The programmer can be programmed to send the Smart's hot water to just one of these circuits, or two or three. The two heating circuits correspond to (1) the ground floor zone of the house (2) the upper floor zone comprising the first and second floor. In addition we have a further time switch which controls flow into the radiators in our large ground floor sitting room. First thing in the morning, the Smart's water goes exclusively to the upper floor radiators, then exclusively to the whole ground floor of the house (Tai Chi time in the big sitting room for Liz), then to the hot water and the ground floor excluding the big sitting room. In the evening, there is a broadly similar heating schedule for the zone. This heating schedule means effectively that the Smart spends most of its time for each zone climbing up towards 70 degrees. Soon after it reaches 70, the programmer switches it to heat another zone and its water temperature falls back to the low 60s. Our zoning system is economical in that we do not heat rooms when we do not want to heat them. It also helps us to use the Smart well in our house which is theoretically too big for it. But I believe that it results in the Smart giving a higher proportion of its heat to direct space heating and a lower proportion to the central heating/hot water.
4. We can identify an upper bound for the Smart's direct space heating output by taking the kilowatt capacity of the radiators in the kitchen and adjacent dining room which we have been able to switch off because of it. These are sizeable double panel double-finned radiators and their total capacity is 9.9 kilowatts. This 9.9 kilowatts is calculated for T60 (i.e. a 60 degree difference between radiator water temperature and surrounding room temperature), and the radiators would rarely reach this output. For information, the kitchen is 4.6 by 4.8 metres and the dining room is 5.3 metres by 4.6 metres. Furthermore the dining room, has a high coombed ceiling which is over 5 metres high at its apex (the floor of the first floor of the dining room wing of the house was removed to create this space). With the Smart we have no need for radiators in the kitchen and only have one small radiator of about 1.8 kilowatt capacity switched on at the far end of the dining room.

To give an upper bound for space heating, and thereby an upper bound to efficiency, I have hypothesized that at its maximum output (level 5) the Smart will provide a direct heat output to space which is equivalent to the T60 output of the radiators it replaces in the kitchen and dining room. I have hypothesized this because so far, at lower levels of output, it has provided a good functional replacement for the radiators. Whether this hypothesis is anywhere near correct will be tested when the outside temperature goes down to 0 degrees or below. The implication of the hypothesis is that for every 1kilowatt to water there will be .566 to direct space heating (at maximum output the Smart would give 12.8 kilowatts to water and 9.9 kilowatts to surrounding space)

Here is a summary of our first lunar month of heating, including lower andupper bounds for efficiency:

Thus the efficiency I think we are getting is lower than Klover's claimed 90.1-92%. An explanation for this may be that the flue from the Klover goes intoa traditional chimney flue which is approaching 13 metres high (when I sweptthe old flue before the Smart was installed, I needed13 metre-long sweeps rodsto sweep the flue from the bottom to the top of the chimeny spot). The flue waslined and insulated as part of Greenflame's installation. Nevertheless theheight of the flue must give a powerful draft. Thus we may be losing more heatup the flue than would be lost in a standard house. If so, we are happy withthis. Part of our reason for installing the Smart was to provide some heat inthe stone wall to help keep it dry. However, part of the explanation may bethat manufacturer's figures are measured in carefully contrived situations(think of car fuel consumption figures). I doubt of Klover's figures areunusual in this regard. I have seen claims that the figures quoted forcondensing boilers are not achieved in actual installations.

For what it is worth, our current extrapolation is that the cost of pelletfuel to heat the house for this year will be £2000 or below, whereas it was£3000 last year with oil together with £350 for wood. There will also besavings in bottled gas for the hob (this cost about £100 last year). We thought that there might also be savings on electricity, but so far we thinkthat there is not much difference. Our savings on using electric ovens andkettles may be balanced by the cost of electricity to start pellets burning,the cost of the central heating pump running for longer (the Smart is much lesspowerful than our oil boiler and consequently the system pumps for longer), theextra cost for the fridge and the freezer because the kitchen is warmer, andother small electrical costs (the Smart's computer and auger and the meter).

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