As environmentally-conscious engineers, we here at Glew Engineering do what we can to save energy and resources both around home and around the office. This might mean choosing products that are more environmentally friendly or energy-efficient. It might mean using our surroundings to our advantage, like pulling cold air through a home or office at night so the building needs less air conditioning the next day. The most satisfying thing, though, is to employ our knowledge of mechanical engineering, materials science and thermal management to design custom hand-tooled solutions. In the next few blog posts, I’ll review some of the current in-house engineering projects that are underway here and maybe give our readers a little inspiration to apply similar solutions in their lives.
Thermal Insulation for an Espresso Boiler
We have recently had energy efficiency on the mind while making our morning (and late-morning and afternoon) espresso. The Glew Engineering kitchen is equipped with an Astra Gourmet Auto, which makes excellent espresso but may use more energy than it needs. The Astra G.A. keeps a permanent supply of super-heated water in order to deliver steam whenever the need arises. The stainless steel boiler is good at withstanding pressure and avoiding corrosion, but its high thermal conductivity means it easily transfers the water’s heat to the air around it. This not only requires the heater to use more energy to reheat the water, but it also increases our air conditioning load in the summer. This is convenient and traditional method for heating cups placed on the top of the machine, as one often may observe, but not an efficient. Our notion is to insulate the boiler, similar to the insulation blankets that many hot water heaters now use (see figure 1). With insulation of a sufficient R-value, the boiler should not have to turn the electrical resistance heater back on as often to maintain temperature. This would allow for much more efficient energy utilization, which will reduce our electricity bill, CO2 emissions, and extend the espresso machine’s lifetime
How Much Energy Could We Save?
In order to measure the effectiveness of the insulation we design, we need to know what kind of energy the espresso machine uses in its unmodified state. It has a 4.2-liter boiler, which it maintains at a pressure of 1.5 atm (around 20 psi) in order to maintain a positive pressure differential. This raises the boiling temperature of the water from the usual 212°F to 270°F. The Astra uses a 2000W heater to raise the temperature and pressure in the tank to the correct levels in about 8-9 minutes. This comes to 0.3 kWh for that first heating period. However, what we don’t know is the power the heater needs to maintain that heat as it is lost to shots of espresso, foamed milk, and kitchen air. For the best comparison, we need to keep track of how many kilowatts the heater uses during a day. We can also extrapolate how much this would increase the AC load as well.
Monitoring Energy Usage
Keeping track of household energy efficiency is a common practice for many people, whether their goal is to save the environment or just to save money on electricity and gas. The most well-known device is the P3 International® Kill A Watt™ meter, which displays not only voltage, current, and watts, but tallies the kWh used during operation as well. However, we soon found out that this device wouldn’t work for our espresso machine. The Kill A Watt™ is limited to 15A and 1875W, both of which are exceeded by the espresso machine’s heater, which runs at 16.6A and 2000W. (You can get a sense of the Astra’s higher power just by looking at its power cord: it’s over half an inch thick). In general, most appliances in the US operate below 15A, so the Kill A Watt™ and its competitors work fine. However, this also means it is nearly impossible to find a similar power meter that is rated for 20A. So, our solution is to build our own. My initial design for the device is shown as a render in Figure 2. Although the materials only cost a little more than a more than the Kill A Watt™, ours will be capable of handling 20A and 4500W. Also, with the longer power cord the screen can will be easy to view even if the power outlet is difficult to access. In the next blog post, I’ll explain my process behind designing and building a small device like this one.