I suspect 60dc120 means 60cm high 120cm long double convector.  SC single convector.

Do you know how single/double convector relates to Type 21 or Type 22?  Does that relate to SC and DC respectively - sounds feasible?

Not exactly.  Type 11 = 1 panel, set of fins, type 21 = 2 panels 1 set of fins, type 22 =  2 panels 2 sets of fins.  Unfortunately SC could be 11 or 21 and DC could be 21 or 22.  I just dont know the Octopus terminology. 

You may be able to deduce it from the variants on the list, or alternatively from the output.   Radiator output is proportional to deltaT to the power 1.3, and 1W = 3.41btu/hr so conversions could in principle be done, but it might be simpler to ask

It seems SC = K1 = Type 11 and DC = K2 =1 = Type 22

If I want the room that is 16c to be held at 21c I could expect the other two rooms to be overheated (by 5c?) and the efficiency to fall through the floor.  I don't even know how I would achieve this under a weather compensation set up

No to the first.  You can reduce the temperature of the other rooms by adjusting the lockshield valves.  You have to do this anyway because radiators are never perfectly sized.  This is called balancing and is part of the installation process although, because it takes time (hours or days) to get spot on often needs to be finished by the homeowner of it is to be done properly.

However you are correct that there is an efficiency penalty because you will have to run at a higher flow temperature.

they recommended changing the radiators initially and I managed to convince them no to , and that wast needed.

the main lesson for me is tha: the heat loss studies not fact and likely a bit conservative . 350 days of the year the temp will be above the design temp and you will be able to get it above design temp (or lower flow temp).
At -5 outside my house is maybe 19.5-20 at 39c flow so on those days maybe a jumper inside but still plenty warm. I could bump flow but I take a jumper over my extra costs .

I wouldn’t sweat it too much . For instance you could balance the heat per room with trvs (although ideally you will keep as much on at low flow temp), or heat upstairs as you switch downstairs off the last hour before bed time, so you move the heat upstairs. 
I suspect most likely you will have a comfortable home though with a bit of configuring after the first few weeks 

There’s a guide to radiator balancing on this forum.

Notwithstanding the advice to sleep in cooler rooms at 18c

@andrewj Earlier with the gas boiler and Tado TRVs controlling the temperature, I used to think 18 is the right temperature. As otherwise the room used to get quite hot. But, with the heat pump the room temperature is steady, and our bedrooms are designed at 21 degrees. To be honest, I am actually liking this. There are no cold spots and it feels comfortable throughout the night. Maybe, a bit warmer for our dog, and I thought she will pant and keep us awake. But, even she is sleeping quite well.

• if every room had a radiator sized to that spec, as the outside temperature increases, heat loss reduces and so does flow temperature and each room maintains its 21c temperature.  
• I don't need to do anything to any radiator to adjust its output and the whole house has the same temperature throughout
• If I wanted to cool the bedroom at night I could either (a) set a setback temperature and the whole house would cool; or, (b) put a TRV on the bedroom radiator and turn it down (or use a smart TRV to reduce and then raise in the morning)

Now let's say I have a house with 3 rooms with design temps of 16c, 18c and 21c and the radiators are sized to give that temperature at a flow temperature of 50c at -3c outside temperature then:

• Each room, regardless of the flow temperature/outside temperature, is at a different temperature relative to the design temp ratio.  As the outside temperature increases, the flow temperature decreases and the rooms maintain their design temperatures.
• If I want the room that is 16c to be held at 21c I could expect the other two rooms to be overheated (by 5c?) and the efficiency to fall through the floor.  I don't even know how I would achieve this under a weather compensation set up
• Assuming the bedroom is the one with the design temp of 18c then either (a) I do nothing because it is already at that temp; or (b) I have to reduce the flow rate back to something-or-other.

The first scenario I understand and it seems logical.  The second, with varying design temps, I don't understand and I don't see how I achieve temperature normalisation in an efficient manner.  I'm not so bothered in this about whether the flow temp is 50c or 40c I think that really relates to efficiency and cost of running.  What I'm trying to understand is how I achieve a comfortable temperature of 21c throughout the house so my wife isn't walking from a warm area into a cooler area.  To me, that must mean every room having the same design temp and appropriately sized radiator.  I hope I'm explaining this ok.

@jamespa  I have already started trying to do a radiator comparison so will wait until I speak to Octopus tomorrow or later in the week.  My fundamental question though is as above.

I suspect 60dc120 means 60cm high 120cm long double convector.  SC single convector.

Do you know how single/double convector relates to Type 21 or Type 22?  Does that relate to SC and DC respectively - sounds feasible?

Not exactly.  Type 11 = 1 panel, set of fins, type 21 = 2 panels 1 set of fins, type 22 =  2 panels 2 sets of fins.  Unfortunately SC could be 11 or 21 and DC could be 21 or 22.  I just dont know the Octopus terminology. 

You may be able to deduce it from the variants on the list, or alternatively from the output.   Radiator output is proportional to deltaT to the power 1.3, and 1W = 3.41btu/hr so conversions could in principle be done, but it might be simpler to ask

There's several design principles which vary from designer to designer. 

The ones Octopus have designed to are generally considered the minimum comfortable temperatures for the rooms you have described. Eg a Gym might either be unheated or only heated to a max of 16 degrees, if that (imagine trying to bench in a 21 degree room!) and a bathroom might want 21 deg or even 22. 

If one is looking to keep the heat pump minimally sized, this might be the approach to take, for me personally unless the client has explicitly consented to lower than 21deg in a room, heat loss and emitter sizing is on the basis of every room (excluding obvious ones like gyms, stores, garages etc) going up to 21 deg. 

The emitter sizing is generally tailored to the room design temp, eg at a given outdoor temp say -2, the emitter at the design flow temp for that outdoor temp on weather comp will be sized in terms of output to reach that room design temp. 

We know the equation Energy = Mass  x Constant x (T2 -T1)

In this case to calculate heat loss simply we use 

rate of heat loss over time = U value x Area x (Temp room-outdoor temp)

Which is a slightly different version of this formula

For radiator sizing, which is essentially what your query is relating to, we must size the emitter accordingly to match the rate of heat loss over time (Q) which for now we will take as a combination of fabric and ventilation losses

This relationship, assuming no minute losses, is related by

Energy in must equal energy out to maintain room temp 

Energy supplied by a rad is simplistically defined by: 

Energy supplied by rad = coefficient of material x SURFACE AREA x (mean water flow temp - room temp)

What's the connection? The only variable we can change is the mean water flow temp if we want to maintain our given room temperature.

Remember that as we increase the dT across the heat pump (by increasing the average flow temperature across the rads, which links to our above relationship) we increase the electrical consumption of the unit.

Once a rad is fitted, realistically the only way to increase the output is to increase the flow temp since everything else can't be changed. Changing mass flow rate doesn't have that much of an impact so we can disregard this.

Pre-install, to increase the energy provided by the rad but maintain flow temp on the lower end (which we know is linked to HP efficiency intrinsically) we can increase the working surface area of the rad, its size. 

What this boils down to I believe, in your case, is that Octopus have seemingly designed to a (max?) 50deg flow temp which is higher that I would personally recommend to get the best efficiency out of your system. This may be to keep the HP size smaller or to reduce the emitter sizes. 
Depending on what unit you are having fitted, if you decide post installation you want warmer rooms you can increase the flow temp but if other rooms have emitters sized to 21 deg and you increase the whole system flow temp you will need to restrict the flow rate to those rooms to keep the temperatures under control. 

Overall you will reduce the system efficiency. 

I hope that makes sense. I try to keep the maths out of it but often it makes the most sense to people to see it laid out in this way. 

Best, 

Rob at Cirrus Energy

www.cirrusenergy.co.uk

Do you know how single/double convector relates to Type 21 or Type 22?  Does that relate to SC and DC respectively - sounds feasible?