MCS calculations are sh1t

[JohnMo]

32 minutes ago, Alan Ambrose said:

refuse to be transparent

Not true, anyone can download the spreadsheet from the website. So calculation are transparent.

 

33 minutes ago, Alan Ambrose said:

Let the SAP & HP calculations be transparent and published as open source

Again they are open source, the complete documents are available online. The SAP calculation method is available all the numbers that are used and how they are used. 

 

Most people choose to get a sap report for £75 how much time do you expect to be put into making sure assumptions are correct? For £75 you are getting a cut and paste of the last EPC.

 

I have rejected the EPC rating on the last 3 properties I have sold and told them to correct or not get paid. They were corrected.

 

37 minutes ago, Alan Ambrose said:

MCS charity

That should be challenged - why can they deem themselves a charity?

[marshian]

34 minutes ago, Alan Ambrose said:

Let the SAP & HP calculations be transparent and published as open source so that other competitors can get in on the act. And all the calcs need a thorough review and revamp.

 

100% this esp in bold

 

I'm running a gas boiler at a WC flow temp of 34 deg C at -2

Return temp at 34 flow is 27 Deg C

Boiler after a restart is modulating down to 3.2 kWh and running between 60 and 80 % of the time

 

What would an MCS calculation come up with - a design flow temp of 45 deg and mandate a 9kW heat pump - the room temps would be bouncing of the TRV's acting as overheat limiters.

 

I'd turn the flow temp down to 32 and the ASHP would cycle like a twat and give a COP of 2.5 or less

 

That's just stupid or mad!!! (I've not decided which yet)

[JohnMo]

12 minutes ago, marshian said:

I'd turn the flow temp down to 32 and the ASHP would cycle like a twat and give a COP of 2.5 or less

Sorry that is just plucking numbers out the air. A heat source, is a heat source, as long as the heat emitters are suitably size to get the heat away for a given flow temperature, why would it cycle like a twat. Cycling is not an issue anyway as long as it's controlled. Some of the best performing heat pumps (by CoP) cycle, but it's controlled cycling.

 

@ProDave runs his ASHP at a fixed flow temp, doesn't seem to get any cycling and gets a good CoP. I have run mine in weather compensation, fixed flow temp and all are equally good. CoP suffers, because you run too high a temperature, and/or have uncontrollable cycling.

 

Your setup is fully suitable for a heat pump, even a 9kW one (which can generally modulate just as far as a 6kW ASHP generally), it's generally the same ASHP as a 6kW with different programming.

 

 

[marshian]

5 minutes ago, JohnMo said:

Sorry that is just plucking numbers out the air. A heat source, is a heat source, as long as the heat emitters are suitably size to get the heat away for a given flow temperature, why would it cycle like a twat. Cycling is not an issue anyway as long as it's controlled. Some of the best performing heat pumps (by CoP) cycle, but it's controlled cycling.

 

@ProDave runs his ASHP at a fixed flow temp, doesn't seem to get any cycling and gets a good CoP. I have run mine in weather compensation, fixed flow temp and all are equally good. CoP suffers, because you run too high a temperature, and/or have uncontrollable cycling.

 

Your setup is fully suitable for a heat pump, even a 9kW one (which can generally modulate just as far as a 6kW ASHP generally), it's generally the same ASHP as a 6kW with different programming.

 

 

 

@JohnMo Of course I'm plucking numbers out of the air - my intro even said so "What would an MCS calculation come up with"

 

So a 9kW ASHP can get down to 6kW - so a 6kW min input with a 3.5 kW heat loss at -2

 

That is designing a system to bloody cycle - No?

 

How bad is it going to be at 10 deg C OAT?

[JohnMo]

2 minutes ago, marshian said:

So a 9kW ASHP can get down to 6kW

Not quite what was meant. A 6 kW and 9kW can have the same minimum modulation. So both around 3kW min output. So if you only need 1.5kW they would both run 50% of the time.

 

There is no impact on CoP with cycling, as long as it's a controlled cycle not a short cycle. No different to a gas boiler really. Issues with gas boilers are just hidden by cheap gas pricing.

 

-10 OAT, CoP is about 2.7 at 35 degs. Same flow temp at 7 degs is about 4.5 CoP, same day flow temp 30 is about 5.5 CoP. -10 a hand full of hours per year, 7 degs typical winter temperatures on average.

 

[marshian]

32 minutes ago, JohnMo said:

Not quite what was meant. A 6 kW and 9kW can have the same minimum modulation. So both around 3kW min output. So if you only need 1.5kW they would both run 50% of the time.

 

There is no impact on CoP with cycling, as long as it's a controlled cycle not a short cycle. No different to a gas boiler really. Issues with gas boilers are just hidden by cheap gas pricing.

 

-10 OAT, CoP is about 2.7 at 35 degs. Same flow temp at 7 degs is about 4.5 CoP, same day flow temp 30 is about 5.5 CoP. -10 a hand full of hours per year, 7 degs typical winter temperatures on average.

 

 

 

Thank you for clarifying that - was not aware that 9kW ASHP had potential to modulate down to 3 KW - thought it was 50% at best

[S2D2]

2 hours ago, marshian said:

 

 

Thank you for clarifying that - was not aware that 9kW ASHP had potential to modulate down to 3 KW - thought it was 50% at best

You need to check individual models for this, for the Daikin units Octopus install there are two ranges which determine what the minimum modulation is: 4-8kW and 9-14kW.

 

There's a thead on another forum where someone got Octopus to rip out the 9kW they installed and replace it with an 8kW unit, performance increased hugely due to the minimum modulation being vastly lower on the 4-8kW units.

[Beelbeebub]

3 hours ago, JohnMo said:

I have rejected the EPC rating on the last 3 properties I have sold and told them to correct or not get paid. They were corrected.

 

Had a property drop down from E to F because the assessor wouldn't look in the loft and assumed it had zero insulation and assumed a fake electric fire in the living room which was there to cover the fireplace was active (it's plug was cut off).

 

As it was a rental and we needed it to be at least E, we used another chap who was a bit younger and brought his own ladder. Quick look in the loft (400mm insulation!) and some other corrections and we were back in business

[marshian]

23 minutes ago, S2D2 said:

You need to check individual models for this, for the Daikin units Octopus install there are two ranges which determine what the minimum modulation is: 4-8kW and 9-14kW.

 

There's a thead on another forum where someone got Octopus to rip out the 9kW they installed and replace it with an 8kW unit, performance increased hugely due to the minimum modulation being vastly lower on the 4-8kW units.

 

 

Thanks for this - I went down the replacement boiler route despite being pretty confident my house was ASHP ready simply because I didn't want to end up with a miss-matched set up under MCS and resulting higher bills.

 

What I am considering is a small ASHP in combination with my gas boiler (create a "Hybrid" system) to do the shoulder season heating and possibly HW - there will be no MCS grant application required (it's pretty clear to that the BUS grant is inflating costs for full installs) and I can do the majority of the install myself - just needing an electrician for the electrickery bits

[JohnMo]

8 minutes ago, marshian said:

What I am considering is a small ASHP in combination with my gas boiler (create a "Hybrid" system)

Basically what I am doing at the moment. Running via home assistant. But want to move away from being reliant on internet for heating.

 

Really didn't want to dump a nearly new gas boiler.

 

Just bought a new controller to run UFH and switching a pump for the boiler only, will run boiler on Opentherm operating against a weather compensation curve within the controller. It will switch the boiler off at a set average outside temperature as well. Heat pump will start based on return temp, running weather compensation, so boiler off, heat pump on automatically with zero input. Will be running system on E7.