Third lunar month of central heating
by Unknown - 16:46 on 29 November 2013
Third Month
If you are a newcomer to this blog, it might be best to begin by reading earlier instalments of the blog, perhaps starting from "Why we installed a Smart".
| Total kg pellets used | 750kg |
| Average daily kg (days in residence) | 41.67kg |
| Metered kilowatt hours to central heating/hot water | 1976wh |
| Gross kilowatt hour value of pellets | 3600kwh |
| Space heating lower bound | 706.42kwh |
| Space heating including residual heat | 887.03kwh |
| Space heating including residual heat and further ESBE distortion | 951.45kwh |
| Efficiency at lower bound | 75% |
| Efficiency including residual heat | 79% |
| Efficiency including residual heat and further ESBE distortion | 81% |
| Cost of pellets | £153.38 |
| Potential RHI subsidy | £265.18 |
During this month, we were away for 10 days, so the average consumption per day has been calculated for our days in residence (while we were away heating was switched over to our reserve oil boiler, because we needed a boiler which would run automatically for the whole period, and the thermostats were cut to 13C ). There were three days when our pellet consumption was unusually high, over 50kg. There were two days after we returned from holiday when the weather was cold and the stone walls of the house needed to be heated up again, and one day when there was a force 9 gale outside. For these three days, we kept the heating on for longer and heated more zones of the house. Excluding these three days, the consumption was about 40kg a day. We began the month by running the Smart at a maximum output level of 4, then after about a week we switched to 5. Except for the three days of extra heating mentioned above,we had two daily sessions of 6.30 to 10.30 then 12.30 to 22.30. During this month we did normally use our wood stove in our first floor study during periods when the upper floor central heating zone was off (this had not been necessary in September, nor for almost all of October). We were happy with the Smart's performance throughout.
The following notes are for anyone who wants a technical explanation of the table.
- Using the metered output to the central heating system I can try to calculate the amount of heat that goes to space heating and thereby calculate the efficiency of the Smart 120. The "lower bound" figure is calculated on the basis of Klover's published ratios between output to central heating/hot water and output to space heating for different levels of output. The other figures make allowance for the balance between central heating and space heating being changed by the presence of an ESBE load valve in our system (please see my postings on a "revised calculation" and on the second month for an explanation).
- I think there is another special factor which has led me underestimate of the efficiency of the Smart 120, and it might be especially prominent in the third month. At its maximum output (5) the Smart is designed to put a relatively low proportion of its output into direct space heating, but at its lowest level of output a much higher proportion goes to direct space heating. Since we changed the maximum output level to 5, I have based my "lower bound" calculation on the proportion Klover say to be correct for output level 5, but actually the Smart 120 is designed to progressively reduce its output level as it approaches its target temperature. Therefore it often runs at output level 4, 3. 2 or 1 rather than 5, even though its maximum output has been set to 5. If I made allowance for this factor, then my efficiency estimates would be higher. However, it is difficult to estimate how much to allow for it, so I have not estimated it.
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