E7 Horstmann controller set-up

glocal

My Economy 7 meter switches to low rate 23:30-1:30 and 3:30-8:30. My water heater is an OSO Direct 20 RD, unvented, 250 litres. By the calculations here:

http://forums.moneysavingexpert.com/showpost.php?p=59892973&postcount=5

it could take up to five hours to heat 250 litres from 15 degrees. In practice, we never run out of hot water so toping up wouldn't take nearly that long. There is a Horstmann controller switching on for a little over 7 hours but the problem is I can only set the start time. Here is the dilemma.

If I set the heater to start at 23:30 I will have to hope it's done by 1:30 to avoid using expensive electricity. If I set it to start at 3:30, it will have more than enough time to finish even starting from 15 degrees but the heater switch will remain on for another couple of hours past 8:30, until 10:30. This means that if we use hot water, say at 9am, the heater will top up and use high rate electricity.

I am wondering if I am missing something short of having the E7 meter replaced to eliminate the 1:30-3:30 gap.

TIA

AndyPK

Surly it doesn't take 5 hours!

Replace the e7 timer with a standard timer if your that worried

glocal

These were not my calculations but they look convincing. I cannot monitor what the heater is doing because there is no light on it and doesn't make any noise. The meter is in the basement of the block.

AndyPK

One if these energy monitors could actually be useful to u then!

Richie-from-the-Boro

glocal wrote: »

My Economy 7 meter switches to low rate 23:30-1:30 and 3:30-8:30. My water heater is an OSO Direct 20 RD, unvented, 250 litres. By the calculations here:

http://forums.moneysavingexpert.com/showpost.php?p=59892973&postcount=5

it could take up to five hours to heat 250 litres from 15 degrees. In practice, we never run out of hot water so toping up wouldn't take nearly that long. There is a Horstmann controller switching on for a little over 7 hours but the problem is I can only set the start time. Here is the dilemma.

If I set the heater to start at 23:30 I will have to hope it's done by 1:30 to avoid using expensive electricity. If I set it to start at 3:30, it will have more than enough time to finish even starting from 15 degrees but the heater switch will remain on for another couple of hours past 8:30, until 10:30. This means that if we use hot water, say at 9am, the heater will top up and use high rate electricity.

I am wondering if I am missing something short of having the E7 meter replaced to eliminate the 1:30-3:30 gap.

TIA

- assuming you pay about 6p per kWh on E7 rate
- and your PartL cylinder heat loss will be 1.5 kW [ish] on 250 litres
- you would save 9p [ish] per 24 hours by turning the water heater off altogether
- and save an [ish] portion depending on how many hours of E7 tariff you allow the water to heat up
- its very unlikely you have any control at all over when the cheap rate starts and ends
- and even if you did is 9p per 24 hours worth the trouble, no heat is wasted anyway
- the 9p [ish] per 24 hours [1.5 kW per day (kWh/24h) on a 250 litre cylinder] goes into warming your home

If you have an PartL two element cylinder [and I expect you do] an E7 tariff & water controller will give you 265 days of piping hot 65°C [legionella] with good heat loss characteristics a year for very little cost.

Your existing cylinder should already be [E7] PartL spec, due to the higher than normal storage temperatures the capability of the insulation to preserve the temperature of the water the type of insulation has a very very low standing heat-loss [one kW per day (kWh/24h) on a 125 litre cylinder] permissible thermal transfer rate from the 60mm of insulating foam, modern ones have the additional benefit of recessed immersions and thermostats to reduce even further energy wastage. All dual PartL cylinders have a top up facility [see below] and is usually operated by a standard 60 minute top-up water controller such as the Horstmann unit also shown below.





The top element [top-up-day rate] will give a couple of big sinks of hot water when used, the bottom element [E7-night rate] will give a full bath and a couple of sinks of hot water. Heat loss is not linear to the volume of water, the bigger the mass the slower the loss rate, eg [figured below are 'ish' but about right] :

1 kW per day (kWh/24h) on a 125 litre cylinder
1.5 kW per day (kWh/24h) on a 250 litre cylinder
2 kW per day (kWh/24h) on a 300 litre cylinder

glocal

It will take 1.5kW or a few minutes to top up for heat losses if no water is used in a 24 hours cycle. This applies when we are away on holiday. Otherwise, it will take anything from a few minutes to up to five hours to raise the temperature to 65 degrees from anything down to 15 degrees (if all water is used up). The problem is five hours won't fit into the E7 23:30-1:30 window. The fixed 7 hour block of the Horstmann controller is bigger than the second, 3:30-8:30 E7 window. One solution would be to set the controller to switch on at 3:30. In the worst case scenario, the water will be hot 5 hours later, at 8:30. I could then switch off the heater manually until 10:30 to prevent it from topping up at high rate. But this sounds like a lot of hassle really. I wish the Horstmann controller was a little cleverer.

Swipe

This Horstmann timer has 3 on/off settings so you can program in up to 3 windows. I fitted one for my parents (dead easy) when their old quartz one broke. Plus they are only £29

http://www.screwfix.com/p/horstmann-centaurplus-c17-timeswitch-with-li-ion-battery-back-up/39028

AndyPK

But the one Richie posted has fixed times. (although with some filling in the back, some adjustment can be made.

glocal

Aha! AndyPK, I've been wondering about this. Mine is almost identical to the one Richie posted. Looking closely at the dial I see there is that arched gap and something like those pins you find on old controllers (but I may be imagining it). If that's what they are, these controllers are designed to be adjusted to switch on for less or more than 7 hours, which would make sense of course. Adjusting it to start at 3:30 for 5 hours would solve my problem. But I am not sure these are user-adjusted or how I am supposed to reach them. Any ideas? I will go looking online for a manual now.

Failing that, Swipe's alternative controller sounds good. I may even try to install it myself. It shouldn't be more than a few screws really.

lstar337

glocal wrote: »

Aha! AndyPK, I've been wondering about this. Mine is almost identical to the one Richie posted. Looking closely at the dial I see there is that arched gap and something like those pins you find on old controllers (but I may be imagining it). If that's what they are, these controllers are designed to be adjusted to switch on for less or more than 7 hours, which would make sense of course. Adjusting it to start at 3:30 for 5 hours would solve my problem. But I am not sure these are user-adjusted or how I am supposed to reach them. Any ideas? I will go looking online for a manual now.

But the saving would be so tiny that it wouldn't be worth your time. The thermostat will mean that while topping up the heat it will not be on for anything like 5 hours anyway.

glocal wrote: »

Failing that, Swipe's alternative controller sounds good. I may even try to install it myself. It shouldn't be more than a few screws really.

The cost of a new timer would never be covered by the savings, so you would be wasting money.

footyguy

glocal wrote: »

Aha! AndyPK, I've been wondering about this. Mine is almost identical to the one Richie posted. Looking closely at the dial I see there is that arched gap and something like those pins you find on old controllers (but I may be imagining it). If that's what they are, these controllers are designed to be adjusted to switch on for less or more than 7 hours, which would make sense of course. Adjusting it to start at 3:30 for 5 hours would solve my problem. But I am not sure these are user-adjusted or how I am supposed to reach them. Any ideas? I will go looking online for a manual now.

Failing that, Swipe's alternative controller sounds good. I may even try to install it myself. It shouldn't be more than a few screws really.

The model Richie posted an image of is the Horstmann Economy 7 Quartz

The installation instructions are here
http://horstmann.skywire.org/files/1213/9867/2106/installer_guide_economy_7_quartz_E7Q.pdf

It explains the timer can be set between a minimum of 4 hours and a maximum of 7 hours.

Get a qualified electrician to do it for you if you are not competent.

(Changing the meter won't help - you'll still have the same off peak times)