Storage heater anomoly?

[Nigel Goodwin]

On Friday at work I built and programmed three ESP8266 temperature and Humidity sensors using SHT30's, powered from 18650's and using sleep mode. Every ten minutes they wake up, upload the temperature, humidity, and battery voltage to ThingSpeak, and go back to sleep.

The main reason for doing this, is that we work in a small industrial unit, which consists of a 'workshop' room, and an 'office' room with a door in between that's open during the day, and closed during the night - originally it was one large room, but we got the landlord to partition it when we moved there. In front of the workshop room there's the entry vestibule, which contains a toilet and a small kitchen area, and in front of the office room there's a garage room, complete with roller door.

Anyway, the heating originally consisted of two storage heaters, one in the main room (now in the workshop) and one in the vestibule - the office was unheated, apart from what passed through the open door, and if it was cold we used a fan heater.

The storage heater in the vestibule failed, and the landlord sent a guy out, who ordered a part for it - turned out the part was no longer available, so he arranged for a new heater - which when they came to fit it, was a 3KW convection heater, not a storage one. As we'd already arranged with the landlord, he fitted it in the office room and we placed an oil filled radiator in the vestibule. The convection heater seems quite good, and has a complex time on it, so we've got it set not to come on at weekends, and to come on about half an hour before we arrive, and turn off about when we leave (around 4:00PM). We liked it so much, we bought a smaller one 1.5KW, and installed that in the vestibule, and set the timer the same way as the other one. The garage is completely unheated.

So the reason for the sensors, apart from the 'fun' aspect , was to see what sort of comparative costs and temperatures the different heaters are providing. They have only been running since Friday morning, and here is a graph of the temperatures through that period. I expected the workshop one to increase as it gets the night time boost, but it doesn't seem to be doing so to the extent I would have thought?. Has anyone any thoughts on this?

Be interesting to see the difference Monday morning, when the convection heaters come on?.

One thought I've had, is that the higher temperatures all round on Friday during the day, could be due to the convection heaters, as while the doors between the three rooms are open during the day, the partition wall also doesn't go right to the ceiling, so heat from the office could go over the wall to the workshop, as well as through the door.

 

[Nigel Goodwin]

Just in case anyone was interested?, here's the same plot a couple of days later, you can clearly see when the convection heaters come on in the morning of 15th April, and again on the 16th. It makes it pretty clear that the storage heater isn't really doing a great deal, with the inside temperature varying pretty accurately along with the unheated areas, just tracking a little bit warmer. Yet when the convector heaters come on, in the other rooms, even the storage heater room rapidly increases in temperature (presumably due to the gap over the top of the wall between rooms). I can't help thinking that replacing the storage heater with another convection heater would be the way to go - and is in fact our plan, but it makes sense to wait until the summer, when the storage heater will be cold.

 

[Pommie]

I always find it interesting when you log things like this, they are never what you expect and never stop surprising me.

Mike.

 

[Nigel Goodwin]

I always find it interesting when you log things like this, they are never what you expect and never stop surprising me.

Mike.

That's what we thought, and which was why I did it.

Anyway, following these tests we've been out today and bought another convection heater - we've turned the storage heater off, so just waiting for it to cool down now. As it's approaching the Easter bank holidays, it should be stone cold by the time we get back. Be interesting to see what happens with the storage heater off, and the convection heaters coming on.

 

[Pommie]

I always remember an engineer I worked with. There was a magazine project (elektor??) that had a circuit that kept your central heating pump working for 5 minutes after your boiler switched off so the hot water kept circuiting. He said "what does it matter, it's still heating your house" and the more I thought about it the more I respected his view. Heat is heat. In your case, heat is heat when you need it.

Mike.

 

[Nigel Goodwin]

I always remember an engineer I worked with. There was a magazine project (elektor??) that had a circuit that kept your central heating pump working for 5 minutes after your boiler switched off so the hot water kept circuiting. He said "what does it matter, it's still heating your house" and the more I thought about it the more I respected his view. Heat is heat. In your case, heat is heat when you need it.

Obviously someone paid attention, because modern combi boilers seem to do just that.

 

[rjenkinsgb]

Are the storage heaters just "dumb blocks" or do they have other controls?

The only ones I've had experience with were at my parents house, something like 50 years go.
The were basically large insulated tin casings filled with layers of blocks, plus spiral elements laid through them.

They also had internal blowers that could be controlled by an external thermostat, so the heat output could be controlled to match the room temperature.
That meant they could be heated at night on economy 7 rate but the heat only used during the day when the rooms were occupied.

I'm rather curious how the heat output is controlled on newer types?

 

[Nigel Goodwin]

Are the storage heaters just "dumb blocks" or do they have other controls?

The only ones I've had experience with were at my parents house, something like 50 years go.
The were basically large insulated tin casings filled with layers of blocks, plus spiral elements laid through them.

They also had internal blowers that could be controlled by an external thermostat, so the heat output could be controlled to match the room temperature.
That meant they could be heated at night on economy 7 rate but the heat only used during the day when the rooms were occupied.

I'm rather curious how the heat output is controlled on newer types?

The storage heater is fairly old, it has a number of controls on it, for setting the internal temperature, and for controlling the release of heat through the vents at the top. There is no blower in it.

The convection heaters are simply timer and thermostat controlled.

With the storage heater turned OFF yesterday, it's interesting to watch the change this morning, you can clearly see where it dodn't get the boost this morning. I'll post another graph later.

 

[Nigel Goodwin]

Just started dismantling the storage heater - disconnected the mains OK, took the cover off - bricks too warm yet to remove

Still, at last they should cool down faster with it dismantled.

 

[Nigel Goodwin]

OK, here's the latest graph, interesting that the Workshop and Office are tracking pretty close now, with just the convection heater in the Office working. BTW, the negative 'blip' this morning was when we had the door open, whilst loading a vehicle - and the green trace is where the door is. The partly disassembled storage heater is cooling down nicely now, and while waiting I've rewired the fusebox connection, so the feed is permanent now, and not timed. Just needs the storage heater removing, and the new heater mounting on the wall, and wiring to the fused switched spur.

I've also added a fourth sensor in the unheated garage (just because I could!), that one uses a DHT22, these three use SHT30's, it's currently 18.7 degrees in there. I've got a graph that shows all four, but there's not many yet from the garage.

 

[Nigel Goodwin]

OK, I fitted the new convection heater this afternoon, not that it's needed now, it's quite warm here today - here's the latest graph showing a full week, which now includes the fourth sensor in the unheated garage.