General > General Technical Chat
What is the real story around heat pumps?
zilp:
--- Quote from: Siwastaja on February 24, 2024, 06:35:53 pm ---But clearly different solutions are popular in different countries. The small ones cost just a few hundred €. It's easy to put one in series to get to high enough water temperature if you have an "easy" (and high COP) source of preheated but not warm enough DHW, which is often the case in monoblock air-to-water retrofits in existing systems which did earlier use higher temperature in a tank with heat exchanger as explained by you.
--- End quote ---
Oh, you are talking about a boiler in a tank? I thought you meant just a (flow-through type) boiler with minimal water volume. That should help, too, I guess.
Well, there are man ways to solve this, the important point is, whatever you do, pay attention to legionella!
JohanH:
--- Quote from: nctnico on February 24, 2024, 06:56:23 pm ---That is too low to protect against legionella. And there can be other parasites in the water as well which are chlorine resistant AND can make you quite sick. So I'd keep the water temperature high. However, I can highly recommend getting a thermostatic tap for shower(s) and bathroom sink(s). They are limited to a safe temperature. And it saves quite a bit of water because it reaches the setpoint temperature quicker compared to manual mixing.
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I guess it's very different in different countries. We are spoiled with very clean ground water in all of Finland. In our town it's taken straight from the ground and you can drink it from the tap as is. Everyone does! As for the hot water, in our house it's heated by the ground source heatpump to about 50 degrees C (in a 180 l tank) and twice a month it's heated to 60 C. There's a thermostat after the heat pump that mixes it down somewhat. Everyone that I know have thermostatic taps in their shower. I considered also putting a small electrical DHW tank in series, but it isn't needed for our hot water consumption (I know many does this over here). It's exactly as Siwastaja explained, they are used to "top up" the hot water and to get more capacity. I have never heard of any legionella or any other problem due to hot water over here, so I guess the legislation is enough.
Siwastaja:
--- Quote from: JohanH on February 24, 2024, 07:15:07 pm ---in our house it's heated by the ground source heatpump to about 50 degrees C (in a 180 l tank) and twice a month it's heated to 60 C.
--- End quote ---
This is what everyone "by default" does with heatpumps (ground source or air-water), because it's as implemented by the pump manufacturers, and I know it practically does not cause problems, but it strictly is illegal; the legal minimum continuous temperature is 55degC (of course very short excursions would be allowed, but "all the time except every two weeks" doesn't cut it). Specifically, 60degC is not enough for a "kill" program unless it's very long.
The legal range is here in 6§: https://www.finlex.fi/fi/laki/alkup/2017/20171047 : 55 to 65 degC. It's quite strict and I'm sure 80% of households doesn't meet these limits, yet legionella outbreaks are still very rare, because the actual high-risk region is more like +30 - +45 degC.
Low side of that range needs to be exceeded by the storage tank itself; high side can be shunted down by thermostatic mixing valve as usual.
nctnico:
--- Quote from: JohanH on February 24, 2024, 07:15:07 pm ---
--- Quote from: nctnico on February 24, 2024, 06:56:23 pm ---That is too low to protect against legionella. And there can be other parasites in the water as well which are chlorine resistant AND can make you quite sick. So I'd keep the water temperature high. However, I can highly recommend getting a thermostatic tap for shower(s) and bathroom sink(s). They are limited to a safe temperature. And it saves quite a bit of water because it reaches the setpoint temperature quicker compared to manual mixing.
--- End quote ---
I guess it's very different in different countries. We are spoiled with very clean ground water in all of Finland. In our town it's taken straight from the ground and you can drink it from the tap as is.
--- End quote ---
The same goes for the NL. In most cities the water from the tap is cleaner compared to bottled water. Nevertheless, ground and surface water does contain legionella and it could grow given the right circumstances. Legislation is greatly depending on what kind fo serious outbreak has occured or not. In the NL (around)15 people died in a single incident due to a legionella outbreak so more legislation was put into place.
Siwastaja:
--- Quote from: nctnico on February 24, 2024, 07:28:51 pm ---In the NL (around)15 people died in a single incident due to a legionella outbreak so more legislation was put into place.
--- End quote ---
You mean this one:
https://en.wikipedia.org/wiki/1999_Bovenkarspel_legionellosis_outbreak
Typical legionella cases seem to be:
* Hot tubs that are kept at around 37degC for prolonged times
* Air conditioner systems that stay inactive (still holding large amounts of condensed water at the evaporator) in very warm conditions, then are suddenly turned on
* Evaporative cooling towers people come in close contact with
* Rarely used shower heads in warm bathrooms
* Rarely used pipe stubs in large DHW systems
Household cases where someone only heat their water to 50degC instead of maybe 55 - I don't believe there are cases at all.
Serious cases all share long-term exposure at temperatures around 30-40 degC (optimum for growth) and then something that makes fine mist out of this water so that people breath it in.
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