JimK wrote:
/....system that in peak summer, I'm sending excess heat to bathroom towel
rail once the store has got to 93 degrees C /q
Sounds useful....
What do you get out of them in winter when you really need all you can get?
Jim K
Virtually nothing in December and January although on a bright but cold
day, 3-4kWh is possible.
This maybe all you wanted to know but here is a bit more if you are
interested.
Heat input comes from solar thermal tubes and any excess PV. A diverter
acts to send any spare pv to the immersion rather than export any to the
grid. In the winter, the PV goes to an immersion half way up the tank,
in summer it goes in at the bottom to increase the storage potential.
In winter effectively only the top half of the store is in use with
inputs from boiler and excess PV and extracted from the top via the DHW
heat exchanger. The tank is allowed to stratify. In summer the whole
store is used. Inputs from PV and solar thermal go in at the bottom and
a de-stratification pump can optionally be used to maximise the energy
capacity by the whole store being at 93 C
Summer and winter are simply names for the two modes and not calendar
definitions.
Typically winter mode is used from November to mid March
The control system is work in progress, but at the moment, the tank stat
that controls the boiler is set to 60C and the timer runs the boiler for
20 mins in the morning which gives enough DHW for morning ablutions and
odd needs during the day (we are all (3 adults) at home all day normally).
If there is any solar input, this adds heat during the day and then at
5pm the boiler runs for 30 mins as needed.
If the solar gain has been significant , then the tank stat will turn
the boiler off sooner.
From March to October, it is rare for the boiler to fire at all for DHW
The cylinder is very well lagged (75mm foam) even so measurements show
that it loses 10-15% of its heat capacity over night.
My proposed control system will endeavour to minimise the energy stored
overnight when it has been sourced by burning gas.
The main input to this will be my "calorimeter". This measures the
cylinder temperature at 7 places vertically (the store is 2.2m tall
deliberately to allow stratification), as well as the output temperature
from the TMV (its control knob is not calibrated) and the cold inlet
temperature. From this data, it calculates how much water can be drawn
off before the output temperature would fall below the setting of the TMV.
The calorimeter is all working but just has a display at the moment.
Eventually it will be integrated into closed loop control.
A few pics
Cylinder and sensors:
http://s115.photobucket.com/user/9fi...3b568.jpg.html
Control panel (under development):
http://s115.photobucket.com/user/9fi...34cfd.jpg.html
Calorimeter display:
http://s115.photobucket.com/user/9fi...82e59.jpg.html
top row: cylinder temps top(right) bottom (left)
2nd row: Actual in and out temperatures
3rd row: cold temperature (trough hold-slow rise) and output
temperature (peak hold-slow fall)
bottom row: Processing time mS: calculated volume of useful hot water:
software version number.
As you might have gathered this has been a bit of a 'project' undertaken
to keep me out of mischief since retiring.
There is a bit more of a write up here
http://www.woodworkuk.co.uk/forum/vi...hp?f=9&t=10577
if I have not bored everyone rigid so far!
Bob