The cylinder is set to heat water to 50 Celcius, then someone has a shower using say 20% of the hot water, then the cylinder fills with cold, then the remaining water in the cylinder is too cold for the next person to immediately have a shower. Do I just need to turn up the temperature on the cylinder, or just wait for it to reheat? Or am I missing something?
Just changed from combi boiler to heat pump and hot water cylinder. Hot water running out.
Did you have the system designed properly? So many companies are putting these systems in at the moment without getting them designed. And it's either usually because the customer doesn't know that there's a large cost in the design or the customer wants to go with the company that is $£€1000 cheaper
What makes you think it might not be? Just been professionally specified, installed and commissioned. I'm just not sure I understand how it works.
Because i just know it's an issue in the industry.
Worldwide? I'm in the UK.
Im in the uk. I assumed you were but had a doubt because you posted in a predominantly US sub.
Ah right cool. Is there a better eg UK specific sub for this query? Couldn't find one.
I agree.
OP, how big is the heat pump tank?
150 litres
Ok, I'm gonna rough these volumes.
150l tank at 50c, depending on the individual, isn't all that much when the shower head is potentially using 40c @ 7.5l a minute. Roughly 5-6l of that is strictly hot water, and as that's used it's cooling the tank. After 8 minutes that's anywhere from 40-48l used if the shower is never adjusted because it's cooling. If your groundwater is 15c, that tank is not down to somewhere in the neighborhood of 37-38c.
The heat pump is a slower but more efficient way to heat the water, so while a fully electric 150l heater produces 300l of water in the first hour, the heat pump model may only put out 200l in the first hour.
7.5lts/min is conservative for a mixer shower on an unvented, most mixers deliver 5lts/min minimum and will easily do 20-30lts/min.
In my experience, very few people run their mixer showers at the lowest flow rates.
Admittedly we should all be putting in water saving devices but that’s not what this thread is about.
The OP could run a simple flow rate check by filling a bucket and timing it to get a feel for what their actual flow rates are.
30l per minute is more than an open half inch pipe is going to supply. Unless he has a legitimate 3/4" valve with a wide open pipe, you aren't getting 30l per minute. If that was the case, he'd need a 300l tank to take a 6 minute shower before it got cold
We are trying to advise why the OP might be running out of water.
My advice is that they may have a shower that runs at 20ltmin (straw pole of most max rates of mixer showers sold by screwfix shows that this is a feasible flow rate)
Which given that people are invariably in the shower a lot longer than they realise, I (like you) asked him to question their assumptions on water usage.
The system should have been designed to a reasonable worst case scenario I personally feel that if you were to design a system on a shower rate of 7.5lts min, you are being conservative.
Was a new "heat pump" cylinder installed? If so, what capacity.....150, 200, 300 litres?
What temperature does the heat pump switch to, in domestic hot water priority mode? 55 Deg C?
Yeah 150 litre cylinder. I think it was targeting 60 Celcius flow temp for 50 Celcius DHW.
So you have enough for a 10-15 min shower. If you want to be able to have back to back showers, you'd need a 300 litre tank.
Typically, those have a few different modes at least in the US. There’s an economy mode that only uses heat pump. There’s a hybrid mode that uses the heat pump and will kick on the electric elements if the water gets too cold. And then there’s a mode that just uses the electric elements. You should check which your unit is in. If it’s an Eco mode, you have a lot less hot water capacity than in the other two.
Installer says it shouldn't need the electric element as the heat pump should be able to do it all, so this is the current set up. Good point that I might have other choices. I still think that if the cylinder is automatically topping up with cold, it will take a while to get back up to temp regardless. Maybe it doesn't automatically top up until it's nearly empty, I don't know.
Make sure the hot water timer is on enough and too be honest just have it on constant and use the thermostat They are well insulated and heat pumps run better over longer periods rather than the old fashioned on off timer. Same goes for the heating, set it to 18 degrees and adjust 1-2 degrees either way
UK here, does the cylinder have electric immersions? These need to be used in conjunction with the heatpump to achieve correct temperature and recovery, what size kw is the heat pump?
It does have an immersion heater but the heat pump can achieve purge temp for legionella so immersion should never be necessary.
All heat pumps in the UK are setup to be combined with immersion, I assumed you were in the UK, if you are then you should be using immersion alongside your heatpump
Hot water rises and cylinders are designed to minimise turbulence in the tank when refilling so if the cylinder is 90% hot and you use 20% then I’d expect you have some blending of the cold inlet and the hot water but you should still have plenty of hot water left.
Are you sure you are using only 20% for a shower?
A mixer shower can use between 10 and in excess of 70 litres per minute.
If you like a hot shower (40+ degrees) then you will be using approx 3lts of hot 1lt of cold in the blending process.
Therefore if your shower head operates at 20lts per min, that’s 15lts of hot every min.
In this scenario, Your 150lt cylinder when fully charged at 55degrees can only supply a 10min shower.
To prolong that, you need a combination of hotter water in the cylinder, colder showers and a shower head with a lower flow rate. (Or a bigger cylinder)
This should all have been factored in, in the design stage.
70l a minute? You'd drown
Fitted a 24” head in a guys combined steam/shower room. At full rate, it could shift water.
70l a minute is damn near 20 gallons. How many drains did you have to put in that shower, or did you just use a single 4 inch drain?
Couple of channel drains with 2” wastes.
Turn the temp up.