Heat pump - new radiators and pipes

ComicGeek

Albermarle said:

So, turn your boiler to an output temp that warms your house effectively, and quickly enough, but as low as possible to still do this. In colder weather, mine can take well over an hour... I will also turn my flow temp up and down a few times over the winter period to match large changes in outdoor temps.

 
I do the same, but you also have to keep in mind that if you do not have a combi the boiler flow temperature should not go below 65 degrees, as this is needed to heat the hot water tank to a high enough temperature to kill any legionnaire bugs. ( although the risk in a domestic setting is relatively low) .
So setting boiler flow temperature is a trade off of competing factors. However it is clear that having it as high as possible is not sensible.

Technically a combi could in certain conditions have a higher legionnella risk than a cylinder, as small combis struggle to heat up water in winter, with possibly only a 35 degree uplift and supply temperatures much lower than 60 degrees. A very infrequently used shower on a combi system technically has a higher risk than the same infrequently used shower on a cylinder fed system as a result, but that's not something you will ever hear in a catchy soundbite. 

But it's stagnant water, rather than temperature in isolation, that's really important for legionnella. So a mains fed cylinder that's being used and refilled regularly is not going to have a significant legionella risk regardless of storage temperature. In fact, the lower the storage temperature the less mixing is carried out at the shower/tap, and the more likely that it gets turned over quickly. I keep ours at 50 degrees all year round.

The key thing is flushing through showers at least once/twice each week if not being used regularly (with windows open for a few minutes), and doing the same when you come back from holiday. Heating the cylinder up to 60 degrees for 1 hour each week is also a sensible precaution for the masses, but this was more of a government catch all announcement because some people still have cold water tanks in lofts feeding cylinders - these pose a much higher risk in the summer as they sit at perfect temperatures for legionnella.

ComicGeek

ashe said:

Just curious as have read a bit about heat pumps needing larger rads and larger pipes 

is this not incredibly disruptive as imagine many houses have pipes under flooring which might be tiled, or in walls which might be papered /plastered or behind tile? 

Is it just larger rads of existing types or are they a set type? My partner hates the look of standard rads and last few years we switched them out to nicer looking ones so just trying to figure through how it works when you get a quote for a heat pump, does or basically turn your house upside down for pipes and radiators?

In reality the government was expecting people to upgrade insulation at the same time as changing to heat pumps. So with the actual heating requirement reducing as a result of the insulation, the new rads for the heat pumps don't have to be quite as big.

They never really thought about more modern well insulated houses with small radiators needing any changes. As a country we are still building brand new houses with radiators and pipework completely incompatible with future heat pumps - absolute madness!

Optimum rad sizes for heat pumps and about 2.5 times the surface area of most modern heating systems.

FreeBear

Albermarle said:

FreeBear said:

Albermarle said: I do the same, but you also have to keep in mind that if you do not have a combi the boiler flow temperature should not go below 65 degrees, as this is needed to heat the hot water tank to a high enough temperature to kill any legionnaire bugs. ( although the risk in a domestic setting is relatively low) .

No. You can still run with a low flow temperature even with a system/heat-only boiler. If you are genuinely worried about the very small chance of catching legionella, maintain a water temperature of 50-55°C in the tank for a few hours each week - This can be done by adjusting the flow temperature up or switching on the immersion heater.

When I have read about this before, you often see the figures 60 to 65 degrees mentioned to prevent bugs growing, so I am only going off that . In fact the Health and Safety Executive recommend 'at least 60 degrees'
HSE - Legionnaires' disease - Risk systems - Hot and cold water systems

60-65°C, the bacteria die within minutes. But then you have to deal with the risk of scalding from the hot water.

At 55°C, the bacteria will still be killed off, but it takes hours rather minutes. A handy little graphic -

At a lower temperature, the risk of scalding is reduced, as is the energy consumption.

Albermarle

FreeBear said:

Albermarle said:

FreeBear said:

Albermarle said: I do the same, but you also have to keep in mind that if you do not have a combi the boiler flow temperature should not go below 65 degrees, as this is needed to heat the hot water tank to a high enough temperature to kill any legionnaire bugs. ( although the risk in a domestic setting is relatively low) .

No. You can still run with a low flow temperature even with a system/heat-only boiler. If you are genuinely worried about the very small chance of catching legionella, maintain a water temperature of 50-55°C in the tank for a few hours each week - This can be done by adjusting the flow temperature up or switching on the immersion heater.

When I have read about this before, you often see the figures 60 to 65 degrees mentioned to prevent bugs growing, so I am only going off that . In fact the Health and Safety Executive recommend 'at least 60 degrees'
HSE - Legionnaires' disease - Risk systems - Hot and cold water systems

60-65°C, the bacteria die within minutes. But then you have to deal with the risk of scalding from the hot water.

At 55°C, the bacteria will still be killed off, but it takes hours rather minutes. A handy little graphic -

At a lower temperature, the risk of scalding is reduced, as is the energy consumption.

Useful diagram !
In fact I have the cylinder thermostat set at around 60, and the boiler flow temperature at about the same ( a bit higher when it is really cold) The pipe runs are quite long and it takes quite a while for the hot water to run through, so scalding is unlikely. On the other hand I do not think the whole large tank ever reaches 60 for all of it, so all a bit theoretical. 
However as @ComicGeek also pointed out, the chance of Legionnaires is very low if you are using all the showers regularly and the cylinder is fed from the mains.
I did know someone once though who caught Legionnaires, and it was very nasty.

FreeBear

Albermarle said:

FreeBear said:

Albermarle said:

FreeBear said:

Albermarle said: I do the same, but you also have to keep in mind that if you do not have a combi the boiler flow temperature should not go below 65 degrees, as this is needed to heat the hot water tank to a high enough temperature to kill any legionnaire bugs. ( although the risk in a domestic setting is relatively low) .

No. You can still run with a low flow temperature even with a system/heat-only boiler. If you are genuinely worried about the very small chance of catching legionella, maintain a water temperature of 50-55°C in the tank for a few hours each week - This can be done by adjusting the flow temperature up or switching on the immersion heater.

When I have read about this before, you often see the figures 60 to 65 degrees mentioned to prevent bugs growing, so I am only going off that . In fact the Health and Safety Executive recommend 'at least 60 degrees'
HSE - Legionnaires' disease - Risk systems - Hot and cold water systems

60-65°C, the bacteria die within minutes. But then you have to deal with the risk of scalding from the hot water.

At 55°C, the bacteria will still be killed off, but it takes hours rather minutes. A handy little graphic -

At a lower temperature, the risk of scalding is reduced, as is the energy consumption.

However as @ComicGeek also pointed out, the chance of Legionnaires is very low if you are using all the showers regularly and the cylinder is fed from the mains.
I did know someone once though who caught Legionnaires, and it was very nasty.

Agreed, legionnaires is a very nasty infection, but with only some 400 cases reported annually in the UK, the risk is extremely low. That said, showering in contaminated water is probably the worst thing to do..

markin

Octopus are going ahead with 10mm pipes in some cases with their 'high heat' heatpump, matched with the cosy tariff.