Limiting Power Draw from Underfloor heating system

[renegadeandy]

Hi, we have 4 electric underfloor heating systems in our house, all managed by 4 Thermotouch 5220/5226 thermostats.

We recently had a solar system installed which is working brilliantly.

When we turn on any of these 4 underfloor heating systems the power draw (regardless of area being heating), immediately shoots up to about 3000W. The thermostat maximum load is rated at 16A, which could use up to 3840W.

I would like to find a way to 'limit' the power draw of the heating system. If, for example, I could make the system draw a maximum load of only 8A, or, supply 120v, perhaps through a different thermostat, then we would only draw about 1400W maximum.

If this is possible, clearly, there would be a limitation to the effectiveness, and speed of which heating the floor, but I am not that worried about this, more interested in finding a cost effective way to achieve the limiting of power.

Is this possible? Is my theory valid, i.e that if we found a way to limit the power, the underfloor heating system would still heat up, but just at a much slower rate (perhaps also with a lower maximum temperature?).

Looking for all advice! We are happy to install something before our current thermostats in a schematic sense, or replace the thermostat entirely.

Many thanks!

 

[bernardgreen]

Assuming the heating elements are not self regulating cable and have a constant resistance.

Connecting two zones of equal power in series will put 120 Volts across each zone. This will reduce the power in each zone to 1/4 of the power at 240 Volts, ( W = V² x R ) so in total the power used by the two zones is reduced to half.

This method is used in some industrial heating systems where rapid heat from cold is needed followed by lower heating to maintain temperature

 

[renegadeandy]

The heating elements are Thermonet matts.

Not sure if its this exact one but its similar.

I think what you suggest could work, but I am not sure is an option given these matts?

Are there any other alternatives?(given these are already installed, its not that easy to connect 2 areas to each other in series).

 

[bernardgreen]

The heating elements are Thermonet matts.

These are constant resistance and NOT self regulating cable

 

[Harry Bloomfield]

Are there any other alternatives?(given these are already installed, its not that easy to connect 2 areas to each other in series).

Triac control could manage that, if you are into electronics. Basically, power is switched on for a series of mains cycles, then off for several more cycles. The ratio of on to off sets the heat output. Switching is done at the zero crossing point of voltage. A similar idea to a light dimmer. You just adjust a control knob to set the power level.

 

[renegadeandy]

@Bernard ty for clarity.

Harry - love this idea! Can you suggest a particular unit capable of doing this?

 

[ericmark]

If you have two zones alternating as to which is on, since the floor stores a lot of heat, you could reduce the total by half, but once you start looking at commercial gear to do this, it can get costly, and the first job is to look at what the units cost.

There were some units designed to allow you to use excess solar power by running an immersion heater, which is about the same load as your mats.

But although many ways to do it, cost is the main problem both in the wiring required and the units.

 

[big-all]

as long as you realize the only money saved is via colder rooms and that can be done via thermostat

 

[Harry Bloomfield]

@Bernard ty for clarity.

Harry - love this idea! Can you suggest a particular unit capable of doing this?

Ardunic || Build Anything

ardunic.com

 

[Why Not Indeed]

You want a solar diverter. Not every load can run off one but resistive heating would be fine.
This guy did kits, he doesn't any more but the site has a lot of interesting info about the concept:

Mk2PVRouter - Introduction

A DIY Constructor’s project to build a Mk2 PV Router system for surplus energy diversion.

mk2pvrouter.co.uk

 

[SUNRAY]

Assuming the heating elements are not self regulating cable and have a constant resistance.

Connecting two zones of equal power in series will put 120 Volts across each zone. This will reduce the power in each zone to 1/4 of the power at 240 Volts, ( W = V² x R ) so in total the power used by the two zones is reduced to half.

This method is used in some industrial heating systems where rapid heat from cold is needed followed by lower heating to maintain temperature

Ahem, W=V²/R
EDIT and power will be 25% oops misread your post

Yes it's very common in large heater batteries (measured in multiple tens of KW) in air ducts. As are the triac controllers and they are frequently synchronised to switch several alternately to even out current draw.

 

[bernardgreen]

Ahem, W=V²/R

Obviously my brain was working ( rambling ) on 1/8th power.

Thanks for pointing that out.

 

[SUNRAY]

Obviously my brain was working ( rambling ) on 1/8th power.

Thanks for pointing that out.

A few months back I was helping my grandsons homework and he showed me a pic of the triangles the teacher had drawn on the board

V, W, I², V²
IxR VxI WxR WxR

He was struggling to use the third and getting the wrong answers, you try getting a youngster to believe the teacher got it wrong

 

[RandomGrinch]

a pic of the triangles the teacher had drawn on the board

V W I² V²
IxR VxI WxR WxR

Am I the only one who dislikes this notation?

The usual notation in physics is
P = V x I etc.

and

Power = Work done / time
P = W / t

Perhaps we should just use the SI units instead?

W = V x A or, V = A x Ω

 

[SUNRAY]

A few months back I was helping my grandsons homework and he showed me a pic of the triangles the teacher had drawn on the board

V, W, I², V²
IxR VxI WxR WxR

He was struggling to use the third and getting the wrong answers, you try getting a youngster to believe the teacher got it wrong

Hopefully this works better