Monday, January 10, 2011

Cylinder thermostat fitted

9 Jan '11: The Heat Pump still seems to have a periodic problem of pushing the water temperature too high - and it often then displays a panic red light when the water temp goes over 60º. Having already had the REGO controller replaced in July, I don't know what more I can do. Ice Energy tell me that IVT are not likely to change the ROM for a while, and that IE are aware of an intermittent problem with the HW temperature - the one I seem to have. Most people, it seems don't seem to care much, but I do! and I am trying to set a new low for energy consumption in the coming year.
   Another reason I care is that if the red light shows too often, the GSHP stops fully, awaiting the user to hit 'Acknowledge' before continuing. If this happens when we are away for a week during a cold spell, it could be serious.
   After a year and more with my whole earth-charging experiment - yes, this entire thing started with my attempt to tame this heat pump - I have tried another idea. I've attached a Danfoss cylinder thermostat, £15 worth, to the metal cylinder, and there is a bell wire to a terminal (bottom right in the photo) that simply turns off the hot water heating if the temperature goes above 56º. I shall have to calibrate it through observation and adjustment, as the thermostat goes from 30º to 90º and it's a rotating switch, not digital.
   My one thing to remember will have to be that I should turn the thermostat to high once a month, to allow the GSHP to pasteurise the water, by going past 60º.

Question about the whole thing?
So you ask... is the whole thing futile? Well not exactly. The heat pump is performing far better than last year, and has done so through the coldest December on record. The quickest-to-show criterion of success is the deep ground temperature. One year ago it was 4.70º-5.0º. Today it was 10.4º. Although the last week has been grey and dull, it has not been too cold, and in the last two days, it got colder but with good sunshine in the morning. I am delighted that we have managed to keep the ground above 10.0º.
 I have also improved my procedures for testing. I leave the heating off always for the same length of time, 4 hours, before testing. My results one year ago may have been tested with a shorter rest time, I cannot remember.
  The research has been good fun. I don't know if the annual saving will justify the expenditure, and provide a payback calculation for doing this to other heat pumps, but I am determined to give it a try.

Postscript: This is going to be more difficult than I thought. The water jacket surrounding the water tank has to get hotter than the tank to heat the water within. The thermostat is fastened to the outer jacket, not the inner tank wall. I need trial and error to see how hot the jacket gets when in a heating cycle, to bring the inner water tank up to the correct temperature of about 50º-54º. On the first day of trying, it seems that 70º-72º on the waterjacket seems to be about right for 55º in the tank. (Surplus heat seems to be drawn from any surplus to contribute to heating.).


  1. Reduce your water temperature. If you need to mix cold water with hot water to get your bath temperature right, it is likely that your cylinder thermostat is set to too high. Ideally your thermostat should be set at 60°C/140°F, so it is important to check if it is not set higher.

  2. hello @room thermostat, it's a heat pump, so we can set the temperature precisely, and ours is always set to 51º. this is a perfectly safe temperature for showering and washing, although if we took baths more often, it would take a while to re-heat to do the next bath!


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