On Wed, 29 Nov 2017 12:31:42 +0000, Martin Brown
wrote:

snip

All we need is a heating engineer that knows stuff, both theory and
in practice
** It was 12C @ 9am, now 16C @ 13:45.

This is with 5 of 2KW heaters and 2 of* 1.5KW heaters.

So if yuo wanted the demp to be 16C before the 10am class how many
heaters would we need in total. ?

You need to do the test with two different total power levels to
determine unambiguously what the thermal capacity and other losses are.

John gave him all the help for calculating the room losses but I'm
pretty sure it was more than he could be bothered with (and would
rather bite the hand that feeds him here in the big gaps between
leaning the labs between classes that do that).

The simplest way out would be to use a couple of 2kW air curtain heaters
over the lab doors which will rapidly warm the *air* inside the lab to a
comfortable temperature

He has said fan heaters are not allowed (as it might melt the
snowflakes) but I'm not sure if an air curtain (that I think I also
suggested) would count as such.

instead of these useless convection heaters
heating up the wall behind them and air that immediately rises up to the
ceiling.The room fills with warm air slowly from the top down.

But if they have low ceilings and people moving about?


Any kind of fan heater would be way better than oil filled radiators if
you want to get the room habitable in the shortest possible time.

They do but can't (not allowed).

Those propane powered fan flame things for heating big garage spaces are
pretty good and fast if you don't mind the smell of combustion products.
(I find them a bit scary YMMV)

If fan / convectors heaters aren't allowed ... !

I would still be interested to hear the outcome of the test of leaving
*just* the 1300W element on, to see how long it takes before it
overtemps (if it does at all).

Also, given the 700W element doesn't appear to be protected by the
(same?) overtemp stat, it's possible the rad would cool faster if it
went from 1300W to zero, rather than 2000W to 700. This might get the
heating back on quicker as it's likely the 700W element would slow the
time the heater took to get back down to the point where the overtemp
stat cut back out (in electrically) again (stat hysteresis).

Then I wondered if the alternative 1500W heaters might not overtemp on
full, but noticed they have a smaller surface area (7 as opposed to 9
'fins') and so it would probably be the same issue with them being
'overpowered'.

I've ordered a couple of electronic power controllers to experiment
with my own rads [1]. The aim is to limit the power to that that they
can actually dissipate as they are only going to be used to provide
'background' heating in the bedroom and I'd rather not hear either of
the stats clicking in and out all night. ;-)

Cheers, T i m

[1] And any heat the controllers dissipate will only go into the room
in any case. ;-)