Willis Heating System

[ericmark]

I have only had one bath in this house, we use the shower, so although we have two baths, they are not used, so having more than a bowl full of water heated at first thought, seems pointless, but we had an 11-inch immersion heater, and we would run out of hot water, mainly as no sun that day, so went to 27-inch immersion heater, and not run out since, it can now last a few days.

The Willis one assumes can heat whole tank, but what I am not sure about is what will happen with 200 watt rather than 3000 watt? I can read about stratification as much as I want, but that does not explain speed of circulation, and how it can or can't use free energy to heat up water, well not quite free, as would get paid 12p/kWh if not used to heat the water.

Over or under 4°C water expands, so gets lighter, so will raise, and we want stored water either cold, or above 60°C, so we want the Epilimnion (top) to be at 60°C or higher, and the Hypolimnion (bottom) to be cold, and the Metalimnion layer as small as possible, there are loads on the internet about Stratification, and the layer in a pond or sea, but as to Stratification in a tank.

System type D – DHW storage cylinder with external plate heat exchanger and loading pump.

The DHW loading storage system enables the whole volume of the DHW to be heated to an even temperature throughout the tank by the use of a bronze pump that circulates the higher temperature throughout the whole cylinder. This system offers an increased amount of usable hot water compared to an equivalent volume of the water within system C, as the primary coil within system C experiences a reduction in heat exchanger effectiveness during the charging and discharging phase. This system increases the amount of available hot water whilst improving protection against the risks of legionella by avoiding cold spots between 20 and 45°C within the cylinder.

TIP: Ask the manufacturer for their pressure drop graph of their plate heat exchanger (HEX) and check the pressure drop across the HEX at the design flow rate against the available head of pressure of the primary pump. A 9 kW heat pump could deliver 26 litres per minute.

Not the Willis as uses a pump. the page is interesting but does not really answer the questions.

With heat pumps not being really hot enough, the idea of the immersion heater is returning. Is it really worth all the valves and system to get the water hotter for when heating DHW? When our CH was above 60°C it was not a problem, but with heat pumps, most of the time the circulating water is too cool, and I found the statement that it's cheaper to use the CH boiler to get DHW is a myth, there may be cases where it is, but also many cases where it's not.

To run a 35 kW boiler to get 2 pints of water to wash one's hands, has to be daft, 4 times as much energy goes into heating the heat exchangers in the boiler as what is used to heat the water that comes out of the tap. I find I used around 35 kWh in summer with the immersion heater and 7 kWh in winter every 28 days, in the summer I found my 20 kW boiler would run for around 20 minutes every other day and the water was a bit on the cool side, so used around 95 kWh per 28 days using oil. But that does not take into account any losses in the boiler. I have noticed a drop in oil use, since using the immersion heater.

But I have no way to really measure how much oil used with a 20 minute burn. And when I used gas, I had a modulating boiler, so again no real way to measure.

 

[ericmark]

the 'advantage' being that heats the water in the cylinder "from the top downwards"

I would say it was more to do with the variable metalimnion layer, so one can select either by time or multi tank thermostats how much DHW is stored. For me having the store local to point of use would be a better use of money. i.e. under sink water heater.

 

[Harry Bloomfield]

Something seems to have gone wrong with your typing - since the first and third of those sentences seem to be saying opposite things - the Willis system can either "heat a very limited amount, with the hot water all concentrated just at the very top of the main cylinder" OR "heat all of the water in the main cylinder down to where the Willis cold connection joins the main cylinder at the bottom" - but not both

I meant, exactly what I said - it can do both, the upper becomes hot quite quickly, but the interface between hot and cold will gradually move down the main cylinder. That is the big advantage of the Willis system, in that the amount of heated water can be limited, to what you might need, for your consumption - either by time, or temperature level.

 

[Harry Bloomfield]

I would say it was more to do with the variable metalimnion layer, so one can select either by time or multi tank thermostats how much DHW is stored.

Sorry, I didn't see your submission, before typing my own - but at least we agree on the control methods

For me having the store local to point of use would be a better use of money. i.e. under sink water heater.

The method involving least kw energy is instant, local heat, which is electric. Better, would be an instant gas water heater, at every hot tap, but simply no practical.

 

[Harry Bloomfield]

The Willis one assumes can heat whole tank, but what I am not sure about is what will happen with 200 watt rather than 3000 watt?

I will have to make a guess on that one...

The water will be warm, and a similar amount as produced by 3kw, but obviously not hot. The Willis system would need a heat source, fairly well-matched to its volume,

 

[JohnW2]

I meant, exactly what I said - it can do both, ...

OK, but that was not really apparent from your first sentence, which read ...

The Willis, can heat a very limited amount, with the hot water all concentrated just at the very top of the main cylinder.

the upper becomes hot quite quickly, but the interface between hot and cold will gradually move down the main cylinder.

How does that differ from any method of heating water in the cylinder?

That is the big advantage of the Willis system, in that the amount of heated water can be limited, to what you might need, for your consumption - either by time, or temperature level.

Again, what is unique about that? I was able to do that with my two-immersion cylinder long before I'd even heard of the Willis system.

 

[Harry Bloomfield]

How does that differ from any method of heating water in the cylinder?

As I explained, the usual immersion heater, ALL the water from the base of the element, though there will be a variation, top to bottom. The Willis concentrates the heated water, more at the top.

 

[JohnW2]

I would say it was more to do with the variable metalimnion layer,

I was merely quoting the 'advantage' ("heats from the top downwards") of the Will system on which most 'explanations' seem to major - but it's daft, since it's not unique to the Willis (or any other) heating system.

so one can select either by time or multi tank thermostats how much DHW is stored.

As I've asked, why does that become different if the heater is 'external' to the cylinder?

 

[JohnW2]

As I explained, the usual immersion heater, ALL the water from the base of the element, though there will be a variation, top to bottom. The Willis concentrates the heated water, more at the top.

I don't understand. Warmer water will rise 'to the top', regardless of how (or where) it got warm.

 

[JohnW2]

The Willis one assumes can heat whole tank ...

You may 'assume' that but, as I've said, it's one uncertainty that I'm still ponderingf. It will certainly heat the 'tank' down to the 'height' of the Willis, but I'm not yet sure about below that.

 

[Harry Bloomfield]

You may 'assume' that but, as I've said, it's one uncertainty that I'm still ponderingf. It will certainly heat the 'tank' down to the 'height' of the Willis, but I'm not yet sure about below that.

It will heat it, to where the base of the Willis connects to the main cylinder - which can be much lower that the standard immersion heater reach, in the usual cylinder.

 

[ebee]

As you will have seen, I have at last come to understand to a fair extent - but I am still struggling to see how it really offers anything appreciably different (or 'better') than one can achieve with a 'high immersion (and thermostat) in the main cylinder.

Kind Regards, John

yes agreed , what I can not get is the rest of the "apparent hype" about how it differs too. That is the bit that I find puzzling me

 

[JohnW2]

yes agreed , what I can not get is the rest of the "apparent hype" about how it differs too. That is the bit that I find puzzling me

Same here - but, to be fair, as I've said, the 'apparent hype' appears to largely be very geographically limited (to a small island, with a total population of less than 8 million), as perhaps evidenced by the paucity of on-line stuff about the system. As a general rule, if one asks Mr Google (or one of his friends) about anything, even something extremely 'obscure', one gets countless hits (some of which are usually nonsense) - but, as you could discover for yourself, if you ask him about Willis one gets remarkably little.

 

[JohnW2]

It will heat it, to where the base of the Willis connects to the main cylinder -

Maybe - but, as I've said, I'm still pondering the issue of those lower bits of the cylinder.

which can be much lower that the standard immersion heater reach, in the usual cylinder.

Sometimes. The lower immersion in my DHW cylinder is a 'short' horizonal one, right at the bottom and close to the cold water inlet.

 

[Harry Bloomfield]

yes agreed , what I can not get is the rest of the "apparent hype" about how it differs too. That is the bit that I find puzzling me

The stratification, in a Willis arrangement, is simply much more effective than in the usual, near vertical element arrangement. With the usual element, you get heated water rising, then falling again as it cools, around the outer edge of the cylinder. Hence, you get much more mixing of hot and cooler water. Compare that, with the Willis system, where the heated water, simply goes in the top of the cylinder, with no convection currents from an element to mix it.

Better than the near vertical element, is obviously the multi-element arrangement, where the element can be chosen, to better match the hot water demand.