My nighttime load sometimes exceeds MAX

[Antony]

Good day all,

 

Its been a long time since I last posted here. Hope everyone is well, under the circumstances here in SA.

I seem to be exceeding my MAX load of 60A (13.8kW) lately, with the underfloor heating, late night geyser top up, kettle, etc.

My under floor heating alone reaches 11kW, add the geyser top up and blink.... off goes my power for a few seconds and comes back on, but because my "intelligent" thermostats switch off automatically when the power goes off, the load is instantly reduced and the power comes back on.

I'm wondering just how all these very large houses with underfloor heating to the hilt manage their power loads?

warms regards from a cold Gauteng.

 

Antony

[RikH]

Hi Antony, is this floor heating a pure resistive load? That is a LOT! Why do you heat this way for god-sake? And what is your source? Eskom, inverter?

Have a nice weekend,

Rik

[Bernardf]

I think an 11kW heating system is probably intended for use in houses with 3 phase power connections.

[Antony]

21 minutes ago, RikH said:

Hi Antony, is this floor heating a pure resistive load? That is a LOT! Why do you heat this way for god-sake? And what is your source? Eskom, inverter?

Have a nice weekend,

Rik

That is the accumulated load for 4 rooms

[Antony]

Yes it resistive, already installed (actually it works great) and from Eskom

Edited July 11, 2020 by Antony

[___]

1 hour ago, Antony said:

I'm wondering just how all these very large houses with underfloor heating to the hilt manage their power loads?

I turned my underfloor heating on once just to see if it works (it came with the house). I decided promptly to pretend it doesn't exist. The previous owner also said he never used it.

We use gas for heating, and we dress warmly. But of course, this is the Western Cape, where our temperatures rarely drop below 5°C... even if we complain about it more than anyone I know.

But to answer the question, if I had to manage it, I'd probably use a few Sonoff-POW units to measure the power, and a software solution (aka smart home pffft) to turn off some things and manage the peak. YOu just need to drop something (a geyser, or a floor heater) for a few minutes to survive.

Edited July 11, 2020 by plonkster

[Richard Mackay]

Does the underfloor heating switch on/off when it's on? (like a hot plate of an electric stove does on low/med settings)

[jykenmynie]

A relatively cheap (and plug and play) solution could be to have timers on the geyser. Unless you are in a very specific circumstance, it should be perfectly fine to heat up the geyser for two hours, say from 18:00 to 20:00 (starting say 30min before people start showering) and then just remember not to have the underfloor heating on during the geyser’s slots.

The geyser could then again turn on say 06:00 to 08:00. If the geyser is well insulated, you should have plenty warm water until at least 12:00.

If you then also use warm water in the kitchen, you might put a third time on for it to heat up again.

[Richard Mackay]

There are smarter ways to do this. CBI make ECM (and LCR) products for this purpose:

http://cbi-lowvoltage.co.za/content/cbi-electric-assists-customers-auto-load-shedding

I have a few load control relays LCR 6A which you are welcome to if they will do the trick

 

[___]

23 minutes ago, Richard Mackay said:

There are smarter ways to do this. CBI make ECM (and LCR) products for this purpose:

i did think of those (the most common one from back in the 70s/80s simply dropped the geyser when the stove was on), but they often require some rewiring. If you have space in dhe DB and the heavy loads are all supplied from the same point, that would be the way to go. Simpler. No issues with "oh the MQTT server did not come back up so nothing works" nonsense.

(Happened to me yesterday. RCD tripped again when the power came back. The Rpi running HA did not come back).

Edited July 12, 2020 by plonkster

[jykenmynie]

8 minutes ago, plonkster said:

i did think of those (the most common one from back in the 70s/80s simply dropped the geyser when the stove was on), but they often require some rewiring. If you have space in dhe DB and the heavy loads are all supplied from the same point, that would be the way to go. Simpler. No issues with "oh the MQTT server did not come back up so nothing works" nonsense.

(Happened to me yesterday. DCD tripped again when the power came back. The Rpi running HA did not come back).

This made me look at the incoming volts on my history after loadshedding. It came up to about 228V immediately, but then dropped to 208V and for about 15 minutes struggled to get back to 225V. Would it not maybe be preferable to set the inverter to only transfer back to the grid after something like 15 minutes of the grid being available or does it really not make a difference?

[Bobster.]

On 2020/07/11 at 8:57 AM, Antony said:

I seem to be exceeding my MAX load of 60A (13.8kW) lately, with the underfloor heating, late night geyser top up, kettle, etc.

My under floor heating alone reaches 11kW, add the geyser top up and blink.... off goes my power for a few seconds and comes back on, but because my "intelligent" thermostats switch off automatically when the power goes off, the load is instantly reduced and the power comes back on.

I'm curious about this. I havea 60A main circuit breaker, but if it were to trip it would stay tripped until I physically reset it. So what is automatically resetting here? Or do you have an inverter that can handle 60A?

[___]

1 hour ago, jykenmynie said:

Would it not maybe be preferable to set the inverter to only transfer back to the grid after something like 15 minutes of the grid being available or does it really not make a difference?

Well, that's not really an easy thing to accomplish without some extra work... besides, the inverter will disconnect if it gets out of hand, so I would probably just not bother.

My issue with a tripping RCD is an old one. It has to do with the bonding relay test of the Multi and surge arrestors/EMI filters in appliances. People don't believe me when I tell them, but I have empirically verified it (unplug appliances, at a certain point it stops doing it). The standing earth leakage is low (below 10mA). It seems even the expensive ABB APR-spec RCD has run out of the capability to handle the transient.

When I moved in here, I did notice that the CBI RCD for the house never tripped when I had the inverter just wired to a plug point (just to get through load shedding that first few weeks while the install was still being done), which is something that in my previous house (that had a Hager RCD) was a huge problem. So this is one more cheap thing I can try.

I'm thinking of setting up a test bench with an array of MOVs to see if I can reproduce the issue. Then I can test which RCDs are less prone to this nonsense...

Aaanyway... that is all off-topic.