So in a home of the future heated by a heat pump, am I right in assuming that centrally heated water/thermostatic mixer will be more efficient than an instant-heat electric shower? I realise the issue is complicated by a lot of factors. (For example, in a household of 3, I seem to be the only one willing to use the lower pressure setting on our electric shower, the other two would like our next shower to be even higher pressure than the max setting! We have a Triton 80si which I have just discovered is a pumped electric shower rated at 8.5Kw, but according to the smart meter it uses something more like 7kw. )
In the world of heat pumps you will need a hot water storage vessel, normally a cylinder. The bigger the better as you will probably not be adding much cold to the mix and the hot(ish) water will have to last for all showers used in a several hour period. To get the water to last you will need low flow, low pressure shower heads. If anyone wants a pressure shower tell them to stand under a waterfall.
Hi, I’m new around here. Hope this helps:
Ohmic heating using an emersion coil or instant hot water provides 1:1 ratios of electricity to heat.
Water tanks can use off peak which is typically 60% cheaper per kwh of electricity. The difference between peak and off peak will become more extreme as renewables make up a large share of our energy generation. There will be periods where you will get free energy, and others when even off peak energy will be expensive.
Therfore instant heat, or booster immersion coils, are the worst choice, since they will generate heat during peak hours which will concide with prohibitively expensive energy. These should be avoided at all costs.
Unfortunately, heat pump cycliders are costly and take up valuable space. If you get one, get the largest possible, since increasing cyclinder doesn’t cost very much, the steel tank and a bit of insulation doesn’t make much difference. This is probably not suitable in high population density settings.
One with a secondary return is worthwhile so you can have near instant hot water from the taps - it wastes less water and heat sitting around waiting for the taps to get hot.
I personally do not rate solar heat exchangers for these tanks. Solar thermal, or any type of solar, comes at a high premium at small scales. Multifamily systems are when these systems delivery value, and even then it depends. But that’s an unpopular opinion in some parts.
Try to get the best packing factor per sqm of your cyclinder’s footprint, including necessary access for maintenance - consult your heating engineer. The perfect place would be at the back of a walk in airing cupboard - line dried laundry in a few hours every time, which doesnt need to be ironed, is a godsend to whoever does the chores. Honestly think this would have been standard if there were more female architects in the past.
Dedicated DHW cycliders with their own heat pump will always out perform immersion only cyclinders and instant hot water systems. Depending on the quality of the heat source they are drawing from the SCOPs are often between 3-5.
Ground source and water source are much more stable during off peak hours, so a heat pump providing DHW will have the equivilant of 5-8 because of the discounted electricty. Again, this will likely reach over 10 when more renewables are on the grid. A factor of 10 is a big deal, since in well retrofitted homes, DHW can account to a 1/3 of total energy demand.
My view is that we will eventually be integrating about 1-2m3 of storage per dwelling for a central heating accumulator tanks. It will be necessary in suburban/ rural settings where heat networks will have more of a problem getting higher grade heat distributed over longer distances.
I personally believe this is innevitable because carbon’s only inherent advantage is that its both energy and storage. As water is the cheapest form of energy storage we will ever have, it’s obvious it’ll play a more important role in the future, as we make our grids sustainable the value of storage goes up because the off peak energy is cheaper more often. So I don’t think we have a choice.
Unfortunately we are stuck with water even for heating, as phase change materials are too expensive and have other complications with respect to heat exchange. For AC, it’s a piece of cake, as we have a phase change to ice.
In rural areas without heat networks, a two stage system will be necessary, where the largest heat pump draws heat from about 5 to 50degrees, from ground/water source, for the bulk of central heating, then a secodary heat pump with a different refrigerant will need to operate between 50-80 deg for DHW and higher density storage during more extreme weather events. These are not common at all right now, and are basically still only academic pilot schemes. But, we’ll get there eventually.
Conversely as the bulk of the population gets a large battery that can be charged at the cheapest times the price advantage of those times will decline until there is no longer an off peak.
The large battery to which I refer is otherwise known as an electric vehicle.
1 Like
This is off-topic. Perhaps it worth splintering it off on another thread: “Renewable grid dynamics of the future and how to design our mechanical systems for them”. Because it’s rarely in public debate at the moment.
Li-ion is good for <6hrs and have to continuously charging and discharging to be cost-effective - they’re great at balancing the phase on short time scales, but they’re never going to replace gas turbines, which is the main problem. Currently, there are no cheap options, if I had to guess, I’d say Carnot batteries have the best chance if you aren’t lucky to have a lot of hydro.
We need between 10-100hrs to have fully sustainable grids. Especially here, where we will be very reliant on wind. It takes 100hrs for most weather systems to move on, so being able to wait around that period almost guarantees you cheap wind energy. These longer durations do not get discharged enough for any battery chemistry to be cost-effective, it’s simply cheaper to generate and curtail energy.
Generally speaking, there will always be peak and off-peak due to the diurnal surge, and generation probably always going to be cheaper than having perfect quantities of storage for excess generation.
However, that’s a discussion about renewable grid dynamics.
I don’t see how cars are the solution to anything, even BEVs. If anything, we need to be getting rid of half of them and only use them for individuals from rural to urban transport hubs, typically small, lightweight vehicles, only doing short hauls and certainly not the 1000 mile ranges being marketed right now. Plenty of ways to do it better than our current mess.
Thanks for your input @Tim_Gilbert and @Frank_Reif . In answer to my question - which type of shower to fit, I think we can agree that a thermostatic mixer is the way to go. Thanks!
1 Like
Yup! How to heat the water for the mixer is the tricky bit.
1 Like
Even trickier might be convincing other family members.
A shower is for washing oneself. The rule I taught my children is:
Water on, get wet.
Water off, wash.
Water on, rinse.
Water off, dry off