I use electrically-heated oil radiators to provide some extra warmth in the bedrooms at night (picture the old steam radiators, but with electrical coils heating oil in a radiator). The heater’s temperature changes very gradually when compared to forced air electrical heat. It takes some time for the oil to warm.
I’ve tried to figure out the thought exercise of whether the high or low setting would provide the most consistent temperature level in the bedroom.
Assume that the thermostat would have the same shutoff and start up temperatures between the high and low setting.
Would the low setting allow the room temperature to dip further after the thermostat has closed the circuit?
Would the high setting have some sort of heating inertia that would continue to raise the room temp even after the thermostat has shut it off?
Is there something I’m not considering?
There’s no particular reason I need the temperature consistent, but I would like to satisfy my curiousity!
If you need wattages, BTUs, or room dimensions to solve, just let me know.
So you have two switches. High/Low and a thermostat?
As you seem to understand, the thermostat will switch the heater on at a little under the temperature it’s set at, and off at a little over. I am guessing that the high switch simply makes it heat up faster - ie work at a higher wattage. This should make it more responsive.
I am not even sure why it has this switch. I have a similar heater in our caravan and it has a thermostat and an on/off switch only.
Your overshoot would be dependent on the rate of temperature change in the room. If the heater never seems on, the low wattage would be sufficient as the temperature does not drop quickly. If it seems to always be on, the low setting may not get the oil warm enough and overshoot would not be much of an issue so running on high may be needed. Size of the room also may require modifying the high / low choice as a high setting would heat a small room to quickly and give a large overage to the temperature.
I don’t understand this; if the hi and low settings have the same upper and lower trigger points, wouldn’t the outputs be identical? I think they may have the same start up temps, but the shut off temps between “hi” and “low” should definitely be different.
If the lower setting cut off at say 20C (or the oil temperature that produced that room temp), then you’d expect the temperature drop to be less until the heater came back on, so it would be the opposite. The high setting that cut off at 25C would produce a larger drop until it hit the lower start up temp.
What you may not be considering that the heater can only shut off at either a “low” or “high” pre-set internal temperature, and that it can’t tell what the actual room temperature is. So you’d either have to do some very complex modeling to figure out the effect of the heat output at both hi and low setting on that particular room and all it’s various parameters, or simply take a few nights and try out hi and low settings which will produce 4 rough outcomes given the question you ask:
A) Low setting never gets the room warm enough = Hi is better
B) Low setting gets the room warm enough and flickers on/off which you want = lo is better.
C) Hi setting gets the room too hot = larger fluctuations and Lo is better.
D) Hi setting is required to get the room warm enough and lo doesn’t even work = hi is better.
…missed the edit window… OK I just realized my A and D outcomes are the same, so cut the outcomes to 3… Also, should add that I don’t think the only difference between a hi and low setting on this type of heater is how fast the heating element raises the oil to the same temperature.
Your problem is a basic control theory problem. It’s a course I haven’t taken yet, but I think the rough answer is that the high setting will overshoot more since there’s more hot oil in the heater that is hotter than ambient. So when the ambient air sensor (thermostat) detects the room air is above setpoint, the heater turns off. There is still very hot oil near the heating element and hotter oil in the heater than in the low case, so the room temperature rises a little bit more. Now, when the temperature drops, on the high setting, there is more energy flowing into the oil and thus a more rapid oil heating rate, so it’s also quicker to respond.
So in general, if you plotted the average temperature of the room over time, it would be higher with the higher setting. I want to say it will also swing higher since it’s underdamped.
So if you want more details, you have 2 easy options.
Grab an arduino and a temperature measurement shield. Maybe a flash I/O shield or use a laptop to log the data. You can get generic ones such that this will cost you $20-30. It’s a handful of lines of programming code : essentially, during the loop() part of arduino-c, you just have
This would store a sample every 10 seconds, you would either send it via serial and have a similarly brief program on the laptop or store it on a flash card if you have the appropriate shield. Even if you haven’t programmed much, this is super, super easy and I bet you can pick it up in no time.
Go online and find a control theory class. MIT courseware has one, but it’s probably a bit tough. I can research one for ya if you want, but have to go back to work atm. Have a good one.
Yessir. Technically the thermostat is a dial, but you’ve got it.
The “low” setting draws 600w to heat the oil. The “high” setting draws 1200w. The low setting heats the oil slower, and the high, faster. Otherwise on/off points are controlled by the thermostat.
The low setting is quite capable of warming the room by itself.
After putting more thought into it last night, I’m not sure there’s an answer possible without doing empirical testing. There are too many unknown variables including air volume and temperature change rate.
