Circulation Pump Modes

My DUCA circulation pump has various modes.
Proportional Pressure
Continuous Pressure
Fixed Speed
Auto Adaption
PWM control

I’m trying to get my head around what the best setting is for my system.

Ideally I think I want to be able to use PWM to try and hit 5 degrees dT but that would involve implementing something as we have an Ecodan that doesn’t control the pump.

I assume we don’t want fixed speed as there will be changes in the system as TRVs close and open. I know I should minimise this but the TRVs are needed in our house to stop bedrooms getting to hot as they are upstairs and better insulated than the colder downstairs rooms with suspended timber floors.

What are the pros and cons of proportional pressure vs continuous pressure. I assume you want to keep the pressure high enough to get to the harder to reach places on the system but not unnecessarily high as to stress the pump and waste energy?

Any one understand how the Auro Adapt works and if it would be beneficial? I can find no details. Grundfoss look to have some auto mode on some of their pumps but the details are very high level and don’t say how it actually adapts.

I’d start with auto adaptation.
If that doesn’t work then try Continuous pressure.
(Wont touch Ecodans, not happy with the CoPs that you can get from them and their auto adapt / learn function doesn’t deliver the best achievable CoPs)
Getting a good deltaT also depends upon setting up the lockshields correctly, and how well the rads are sized to match the heat loss and design temperatures.
We’re doing a LOT of works on different pumps in the new year and could give you more of an update at the end of Jan :slight_smile:

Circulators… which one do you have? What ecodan do you have? What flow rate can you get?

Circulator controllers are generally designed for a gas boiler with high temp, low flow and largely closed TRVs. An ASHP is different. You will have a huge flow. And that is the point. We do not have a single TRV.

Do consider a TRV will gradually close and increase the resistance. The goal being that it opens just enough to keep the temperate right.

TRVs do NOT use PWM. Heated floors do. Floors generally have a controller which fully opens for five minutes, then fully close for ten minutes based on demand.

Our MAGNA3 is set to constant curve at 100% for our 8.5kW ecodan. We get a flow of 1400l/hr.

We have a DUCA APE25-8-130 and an Ecodan 8.5kW like yours.
I currently have the pump in Proportional Pressure level 2 giving us around 15 l/min in Space Heating and 20-21 l/min in hot water.

At some point I would like to see if I can wire in the PWM on our pump to the FTC6 to be able to select two a different speed for DHW from Heating from the controller. I’m not convinced the using the same setting for both is the most efficient.

Not sure what other way to regulate the temperature in our house other than having TRVs in the bedrooms. Currently the bedrooms as the most insulated part of the house but the area we want to be colder so the TRVs act to stop the bedrooms becoming too warm when trying to get the downstairs up to temp.
I plan to improve airtightness and add insulation to our suspended timber floor which should help reduce the imbalance in heat losses.

1400l/h (23 l/min) is right at the top end of the 8.5kWh’s flow range, someone over at the Renewable Heating Hub forums (Ecodan ASHP – How to optimise my set up? – Page 2 – Air Source Heat Pumps (ASHPs) – Renewable Heating Hub Forums) has spotted that the Ecodan R32 Data Book has been updated recently to give a range and a recommended of 15.2 l/min.
Although there is no reasoning behind this number given.

I use TRVs on a dual zone Ecodan 14kW running with auto adaptation and it works really well with a flow rate over 31l/m on heating and 23l/m with DHW.

IMHO any control system that ignores internal temperature and relies on inveterate tweaking of lockshields and curves is never going to receive the mass acceptance that’s required for ASHP rollout.

This. This. This.

I removed the lock shields, TRVs and put in a distribution manifold. Utterly transformed the system. Quite a lot of work, though.

I never did find TRVs that work with a PWM control. They all seem to be analogue in that the progressively close/open the valves. Which is perfect for gas, and terrible for an ASHP.

I suspect that the reason for stating a flow rate is guidance for sizing circulators etc. At some point you might cause cavitation inside the heat exchanger. Does the spec state an intended flow rate, or an absolute maximum?

It is interesting that note *1 says the aim is to get a dT of 8K when the preserved wisdom is to get 5K.

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I have no idea what the T20/30 or T17 models are!

I certainly agree that a deltaT of 8C is very large. I wonder what their recommended flow temp is? If they have a flow temp of 45-50, then deltaT of 8C might be possible. When your flow temp is 34C you are not gong to get a return temp of 26C.

Cavitation on pipes occurs when the speed is over 2m/s. You get a lot of noise too.

I think it is the Mitsubishi Hydrobox / Ecodan Cylinder models as that page is taken from that section of the data book. It might be that with that set up there is a specific reason for those values (can’t think what though).

Yea I would have thought flow rate will depend on flow temp and the sizing of emitters as to what the return temp will end up being.

This is exactly right.

Consider emmitters with a mean temp of 35C. You can achieve this by a deltaT of 10C, or a deltaT of 5C. The flow and returns will be 40/30 and 37.5/32.5 respectively. The flow rate will be different.

Both these scenarios will have the same heat output.

The deltaT of 5C is preferable. This is because the ASHP is more efficient the lower it has to heat the water too.