Boiler volume reduction in an espresso machine

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Javierba

#1: Post by Javierba »

Hello there!

I got a expobar g10 1gr for home use.
It is definitely a way too big cannon for a way too small fly but I really like the machine.

My regular use Szenario is a coffee in the morning and a coffee in the noon. I turn on the machine for each coffee, it takes about 30 min to get warm and uses about 0.7 Kwh for the morning coffee, the noon coffee needs usually 0.55kWh as the machine is not complete cold. I have measured as well 0.36kWh per hour consumption when is keept hot. But this is not my use case.

I am looking for ways of making the machine more efficient, therefore I am in the process of insulating the boiler with armaflex ht as many have done before.

Although I am sure that it will help, I would like to reduce the boiler capacity to further reduce the warm up consumption.
The boiler of my machine is 6 liters and is filled half, also 3 liters.

I have thought two possibilities but I am not sure about neither of them:

The first one would be to install a longer water probe, making sure that the heating element stays covered. I don't see many problems associated other than I would have to check that the brewing temperature is not greatly reduced.

The second and more attractive alternative would be to fill the bottom of the boiler with stainless bearings or some other food compatible material. This alternative is more attractive since I could get most of the water out when finished with the coffee. There is about 3 to 4 cms of dead space below the heating element and the water output. The problem I could expect: galvanic corrosion. The boiler is made completely of copper with brass fittings, only the level probre is stainless and is electrically insulated from the boiler.

Does anybody have experience with reducing the boiler capacity?

Regards, Javier

Markant

#2: Post by Markant »

Javierba wrote: The second and more attractive alternative would be to fill the bottom of the boiler with stainless bearings or some other food compatible material. This alternative is more attractive since I could get most of the water out when finished with the coffee. There is about 3 to 4 cms of dead space below the heating element and the water output. The problem I could expect: galvanic corrosion. The boiler is made completely of copper with brass fittings, only the level probre is stainless and is electrically insulated from the boiler.

Does anybody have experience with reducing the boiler capacity?
If you want to go that way, glass marbles might be a good, inert alternative.
Mark

harrisonpatm

#3: Post by harrisonpatm »

Oh man, this sounds like a fascinating mod that I hadn't previously thought of. Boiler size is certainly one of the drawbacks for me when it comes to getting a more powerful machine in my house; such a massive waste of energy for 2-3 coffees per day. I hope someone who knows more than me can answer your question.

I cannot speak to what would happen to ball bearings filling the bottom of the boiler, I don't know enough about materials science. As for changing the probe to cutoff flow at a lower lever, in principal, that shouldn't raise any technical difficulties. My one thought is, if the volume of water is lower, will this affect the steam function? When a boiler is 3/4 full of hot pressurized water and the steam valve is opened, there is a loss of pressure and temperature. When the valve is shut, the pressure/temperature returns, mostly due to the heating element cycling on, but the element is helped (or has less work to do) by the thermal mass of a 3/4 full tank of water and its high specific heat. If you adjust the level probe and the tank is kept at, say, 1/4 full, thats less thermal mass and your steam pressure will take longer to build up. However, if you're only making one coffee at a time, perhaps this isn't an issue for you.

Or I could be wrong (always a possibility). Is the energy required to heat a tank of 3/4 water and 1/4 air, the same as energy required to heat a tank of 1/4 water and 3/4 air, considering the contents of each are kept at pressure?

If you were to fill the tank with bearings, either glass or metal, I would presume the space taken up by them would retain nearly as much thermal mass as water would have, so steam pressure returning would be less of an issue than changing the probe level.

Please post your results of whatever you choose, I'm very interested i how this goes.

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Jeff
Team HB

#4: Post by Jeff »

First, a "public safety message" -- make sure that whatever you do, there's no chance of the element going dry.

https://crem-international.co.uk/expobar/g10-product -- shows a 6 liter boiler, which puts the question in a different light from a home machine with a boiler often somewhere around 1 liter.

How much do you think is [heating and] boiling the water and how much is heat loss from the boiler and group?

0.36 kW (360 W) "hot idle" gives an idea that heat loss is a significant contributor. I vaguely remember my E61 HX idling at around 45 W.

It's too early in the morning for me to figure out specific heat (J/kg/°K) and density of materials (kg/liter), but it seems that you'd need something that is fewer Joules/cm^3/°C than water.

harrisonpatm

#5: Post by harrisonpatm replying to Jeff »

Alright then, a query, in theory only. Without going into the specifics and doing the math for specific heat calculations. What do you think of reducing the boiler size for a 1-2l "prosumer" machine, rather than the 6l boiler being discussed? For someone only making 2-3 shots a day? Sorry, theres an idea in my head now and it won't leave until it gets some answers?

User avatar
Jeff
Team HB

#6: Post by Jeff »

Without math, my electric kettle brings a liter of water to 208°F in a few minutes (just under local boiling point). Even at our cost of electricity at around $0.30/kWh, that doesn't seem like a lot to me. My E61 HX idling at under 50 W suggests to me that there aren't a lot of gains to be had with a typical home machine, as long as the boiler is insulated.

baldheadracing
Team HB

#7: Post by baldheadracing »

This is a topic that has passed my mind lately.

Unfortunately, I suspect that balls or marbles won't be of much help in reducing warm-up time as they would also need to be heated up.

Insulating a boiler helps more with noon warm-up than the morning's, but is more apparent in reducing steady-state energy consumption. As an example, suppose that you wanted to leave your machine on all morning. Effective insulation would reduce the cost of that convenience. (I do wonder a bit about the impact on temperature performance if insulation was added to an existing HX. )

Less water does warm-up faster than a full boiler. I have done that on manual fill machines (with a sight glass). However, unless I actively flush during warm-up, the groups take the longest to get to operating temperature on my machines.

If you do want to lower the water level, then, if you don't have one, I would consider getting a flexible borescope that displays on your phone. That will let you see exactly how low you can go. They're astonishingly inexpensive.
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

Javierba (original poster)

#8: Post by Javierba (original poster) »

wow, first of all, thank you all for your answers!
Markant wrote:If you want to go that way, glass marbles might be a good, inert alternative.
Mark
this is a great alternative, one think i did not mention is that you need a really big amount of bearings to sum up some volume, which makes the stainless bearing not very cheap. For amounting one liter with 1,5cm marbles/bearings you need about 565 of them...
harrisonpatm wrote:If you were to fill the tank with bearings, either glass or metal, I would presume the space taken up by them would retain nearly as much thermal mass as water would have, so steam pressure returning would be less of an issue than changing the probe level.
The specific heat of water is pretty high, that is to say, the amount of energy needed to bring water to temperature. although you are right that it will take some energy to warm up the marbles/bearings, the specific heat of glass is 800 J/kg°C, the specific heat of stainless is 500 J/kg°C and the specific heat of water is 4200 J/kg°C. since i want to displace some volume, you have to account also the density of the material, glass is 2500 Kg/m3, stainless is 8000 Kg/m3 and water is 1000 Kg/m3. If you do the numbers, you get that for warming up a liter of water one degree you need 4200 Joules, one liter (or dm3) of stainless 4000J and one liter of glass 2000J.

It looks like the stainless idea was not good after all...
harrisonpatm wrote:My one thought is, if the volume of water is lower, will this affect the steam function? When a boiler is 3/4 full of hot pressurized water and the steam valve is opened, there is a loss of pressure and temperature. When the valve is shut, the pressure/temperature returns, mostly due to the heating element cycling on, but the element is helped (or has less work to do) by the thermal mass of a 3/4 full tank of water and its high specific heat. If you adjust the level probe and the tank is kept at, say, 1/4 full, thats less thermal mass and your steam pressure will take longer to build up. However, if you're only making one coffee at a time, perhaps this isn't an issue for you
yes, if you reduce the amount of water in the boiler you are not going to be able to have the steam valve open as long without waiting to warm up. But keep in mind that a regular E61 for home use has a 1,7L boiler usually filled with around 0,8L of water. If I manage to reduce the boiler volume one liter with glass marbles i will still have the thermal mass of 2,5L (recalling the specific heats above). And as you said i do not make many coffees
Jeff wrote:How much do you think is [heating and] boiling the water and how much is heat loss from the boiler and group?
From the energy consumption measurements i have done, i found out that, during the first heating of the machine, from cold to first time hitting run temperature, it takes about 15 minutes and consumes 0,4 -0,5 Kwh depending on morning or noon coffee. The amount of energy needed to warm up 3 liters of water up to working temperature (from 20°C to 120°C) is 0,35Kwh. if i manage to replace one liter of water with glass marbles this number goes to 0,3 Kwh.

For reference, before i bought the Armaflex insulation i did some calculations of what kind of energy reduction i could expect,
i calculated that during the first 15 minutes, 0,045 Kwh are lost due to heat loss. between 15 and 30 min the machine losses about 0,09 Kwh.
So, the theoretical amount of energy that i could theoretically spare if i got the perfect insulation is 0,135Kwh.
Jeff wrote:0.36 kW (360 W) "hot idle" gives an idea that heat loss is a significant contributor. I vaguely remember my E61 HX idling at around 45 W.
I think this number is a little bit off, i measured my old Gaggia before selling it, and i measured arround 60 W, A friend of mine got a rocket espresso, but with the current situation i havent manged to storm his flat, powermeter in hand

JRising
Team HB

#9: Post by JRising »

I'm with Baldheadracing.
Just changing the water to stainless steel by putting things other than water into the boiler won't greatly change the thermal properties of "the boiler and everything in it". You would have to insulate the ball bearings so that they're not drawing heat out of the water if you want to just reduce the thermal mass of "the boiler and everything in it that the element needs to heat". What's more, stainless steel sinks and proves itself to be denser than water, so it's actually more thermal mass than the water it has displaced.n The amount of cold water coming in to displace the brew water out is... Well, you know.

Theoretically, in a multi-brewhead, HX machine, one could empty all but one heat exchanger and only use the non-emptied brewhead to simulate reducing the thermally conductive "boiler and everything in it" but the electricity savings aren't anywhere near what one would see in buying a single brewhead machine if that were the size they needed.

The insulation is a good idea. Insulate the boiler however possible so 'the boiler and everything in it' aren't leeching out heat to mounting bolts, brackets, brass pipes touching body, etc.

harrisonpatm

#10: Post by harrisonpatm »

The takeaway i'm getting is, there's a lot to takeaway! Lots of variables besides just the math: what machine are you using, what is your coffee consumption, what are your goals, ect. Which is fun to think about and fascinating.