Octopus Heat Pumps

Reed_Richards

My system was designed for a flow temperature of 50 C; it's not the end of the world. 

• Because I use Weather Compensation it is very rare indeed for the flow temperature to get near to 50 C (except for the DHW).  
• And from my WC settings I can see that that I only need a flow temperature of 45 C at my design operating temperature of -4 C; my heat loss must have been over-estimated.
• I'm also fortunate to have a heat pump with a large modulation range so I can access the modest electrical power draw that you need when it is warmer outside.

With the benefit of hindsight, I would have tried to influence the design to achieve a lower flow temperature, but I might not have succeeded.  As it is, I have two rooms where the radiators are a bit undersized and at the time I could not see how to overcome this.

My heat pump has a dedicated electricity meter but no heat meter.  By comparison with my old oil boiler I can see I must achieve an SCOP of approximately 3 but that's the best that I can tell. 

stripling

Spies said:

matt_drummer said:

Spies said:

They are putting massive emitters in our house as it is, two 1400x600 k3 radiators in the front room, K2's everywhere else

What is your total radiator output on their radiator schedule?

It will be at dT30c more or less.

6127w of which 2892w is the living room. 

The living room is very tall with an insulated pitched roof

So it may be slow to get up to full heat but then if the pitch is well-insulated it should be fine. I find when I light my wood burner that the heat gradually penetrates the whole bungalow and yet it's not a huge stove.  

Spies

matt_drummer said:

Spies said:

matt_drummer said:

Spies said:

They are putting massive emitters in our house as it is, two 1400x600 k3 radiators in the front room, K2's everywhere else

What is your total radiator output on their radiator schedule?

It will be at dT30c more or less.

6127w of which 2892w is the living room. 

The living room is very tall with an insulated pitched roof

Is your front room nearly half your total heat loss?

Just for a comparison, I have about 30,000W of radiator output at dT30c

Hopefully this answers any questions, just bear in mind they way they list the rooms with multiple radiators, they show the total room loss on both

matt_drummer

Spies said:

matt_drummer said:

Spies said:

matt_drummer said:

Spies said:

They are putting massive emitters in our house as it is, two 1400x600 k3 radiators in the front room, K2's everywhere else

What is your total radiator output on their radiator schedule?

It will be at dT30c more or less.

6127w of which 2892w is the living room. 

The living room is very tall with an insulated pitched roof

Is your front room nearly half your total heat loss?

Just for a comparison, I have about 30,000W of radiator output at dT30c

Hopefully this answers any questions, just bear in mind they way they list the rooms with multiple radiators, they show the total room loss on both

I know, it caused some confusion when discussing my heat loss.

They only show the heat loss of rooms or areas with radiators too.

This isn't always the total heat loss of the property.

Spies

Every area is covered as the entrance hall one is oversized for coverage up the stairs I believe.

matt_drummer

Spies said:

Every area is covered as the entrance hall one is oversized for coverage up the stairs I believe.

Yes, but the stair area will have a heat loss too, the heat losses on the radiator schedule will not be the total heat loss.

There may also be an unheated area at the top of the stairs, a landing maybe?

My problem all stemmed from a conservatory where the original surveyor put it down as having a tiled roof. After initially saying it couldn't be heated and needed to be excluded he then proclaimed all was OK! It didn't even need a radiator change according to Doug the surveyor!

Spies

Ah ok I see your point.

Another thing I can't seem to get my head around is that if you increase flow temperature to 55c you increase radiator output, but then you lose heat output from the heatpump, are those two factors not fighting each other?

Reed_Richards

I don't understand the radiators shown as *Center (and we don't spell centre that way here).  Why don't they state the proper type and dimensions?  It makes it harder to understand what you are getting and so whether there is scope for a radiator with a larger surface area.

Edit: Oh CenterRad or Centrebrand, presumably.  But the ones listed here: https://www.radiators.co.uk/brand/centerbrand have the type and metric dimensions given.

matt_drummer

Reed_Richards said:

I don't understand the radiators shown as *Center (and we don't spell centre that way here).  Why don't they state the proper type and dimensions?  It makes it harder to understand what you are getting and so whether there is scope for a radiator with a larger surface area.

Center Rad is a brand.

I just sold the one they fitted in my hallway that I replaced in December.

matt_drummer

Spies said:

Ah ok I see your point.

Another thing I can't seem to get my head around is that if you increase flow temperature to 55c you increase radiator output, but then you lose heat output from the heatpump, are those two factors not fighting each other?

I am not sure I understand your question.

But I'll have a go, there comes a point where the heat pump can't get the water any hotter and as it approaches that point it has to slow the flow rate.

Heat produced is a factor of dT between flow and return and the flow rate.

In theory more flow temperature will give more heat as long as the return doesn't increase too much, but if the flow rate decreases then eventually you'll end up with less heat produced. You're at the limit of the heat pump's ability to heat water.

Think of it a bit like the power curve of an internal combustion engine. As the revs increase the power rises but it reaches a point where the power drops off even though the revs are still increasing, and then it reaches the rev limiter or goes bang!