Slope weather curve and questions

Reed_Richards

matt_drummer said:.

The room temperature is irrelevant.

So no Load Compensation option with Daikin heat pumps?  My LG heat pump will do this, although I hadn't realised until I set it up for a 3rd party controller and that overrides the Load Compensation option.  I keep thinking I should alter the jumper that would enable Load Compensation but I've never quite been brave enough.

ninjaef

Reed_Richards said:

matt_drummer said:.

The room temperature is irrelevant.

So no Load Compensation option with Daikin heat pumps?  My LG heat pump will do this, although I hadn't realised until I set it up for a 3rd party controller and that overrides the Load Compensation option.  I keep thinking I should alter the jumper that would enable Load Compensation but I've never quite been brave enough.

in English please for all of us who are not scientists 

matt_drummer

In fan coils you can adjust the dT between 1c and 10c I believe.

Radiators is fixed at 10c.

A lower dT will result in a higher flow rate, the slower the water flows through your radiators the more heat they will lose giving a higher dT.

The amount of heat delivered by the heat pump is calculated using the dT and the flow rate and they are directly related to each other. Basically how much water cools by how much in a set period of time. That is how heat pumps can run at low flow temperatures using large radiators. It is not the actual temperature of the water that gives out heat, it is the change in the temperature and how much water changes temperature that determines the heat delivered. Water flowing at even 70c through radiators won't give out any heat unless the water actually cools down whilst flowing through them.

4kW of heat at a dT of 5c will have double the flow rate of 4kW of heat dT 10c

Too low a dT may result in the heat pump not being able to flow water fast enough to maintain the requested dT.

Too high a dT will mean that the water will always be flowing at the slowest rate possible and the requested dT will never be achieved.

I run as radiators and never get a dT of 10c as my flow temperature is only ever at 33c at the highest. But, I have full monitoring and can see the results of my fiddling in real time and I have a good idea what I am doing.

A lower dT gives a higher mean flow temperature through the radiators at any given flow temperature and this allows best radiator performance and the lowest flow temperatures.

Here are two examples

Flow temperature of 40c with dT 10c is a mean/average flow of 35c.

Flow temperature of 40c with dT5c is a mean/average flow of 37.5c

The radiators will give out more heat at 37.5c than they will at 35c with the same room temperature.

To get a mean flow of 37.5c at a dT of 10c would require a flow temperature of 42.5c which is less efficient than flowing water at 40c.

That is why a dT of 5c is set, you can go lower but the required flow rate to get the heat required may be too high for the pump or the pipe work.

matt_drummer

Another way to think about this is from the point of view of the heat pump.

In two different scenarios producing the same amount of heat it can either heat 10 litres of water a minute by 10c (that is at a dT of 10c) or 20 litres of water a minute by 5c (at a dT of 5c)

Both scenarios result in the same amount of energy being required.

But as the amount of energy consumed by the heat pump is variable, it generates more energy than it consumes by extracting energy from large volumes of air and transferring it to a refrigerant and then the water, it may take more electricity to heat a smaller volume of water by a larger temperature than vice versa.

A dT of 5c is considered by most people to be the optimum. Lower the dT and you have to heat a larger volume of water less, and raise the dT you have to heat a smaller volume of water by a larger amount to get the same result.

There is a point where the best efficiency is achieved which is why Octopus set it to fan coils with a dT of 5c even though you have radiators.

matt_drummer

Reed_Richards said:

matt_drummer said:.

The room temperature is irrelevant.

So no Load Compensation option with Daikin heat pumps?  My LG heat pump will do this, although I hadn't realised until I set it up for a 3rd party controller and that overrides the Load Compensation option.  I keep thinking I should alter the jumper that would enable Load Compensation but I've never quite been brave enough.

Yes, it can load compensate with the Madoka controller, that is Daikins own fancy room thermostat.

The Madoka monitors how quickly the room is heating or cooling and modulates the flow temperature within adjustable parameters to keep a stable room temperature. It does not adjust the dT to do this.

The room temperature is of no relevance to dT though, it isn't on any heat pump.

If I set my heat pump to run at a dT between flow and return of 5c it doesn't matter whether my room is 17c or 23c, you still get a dT of 5c.

I am sure yours is the same?

smallblueplanet

matt_drummer said:

Reed_Richards said:

matt_drummer said:.

The room temperature is irrelevant.

So no Load Compensation option with Daikin heat pumps?  My LG heat pump will do this, although I hadn't realised until I set it up for a 3rd party controller and that overrides the Load Compensation option.  I keep thinking I should alter the jumper that would enable Load Compensation but I've never quite been brave enough.

Yes, it can load compensate with the Madoka controller, that is Daikins own fancy room thermostat.

The Madoka monitors how quickly the room is heating or cooling and modulates the flow temperature within adjustable parameters to keep a stable room temperature. It does not adjust the dT to do this.

The room temperature is of no relevance to dT though, it isn't on any heat pump.

If I set my heat pump to run at a dT between flow and return of 5c it doesn't matter whether my room is 17c or 23c, you still get a dT of 5c.

I am sure yours is the same?

I'm still confused by what changes the Flow Rate, it must be more than dT? Feel free to correct me as my head feels like it is stuffed with cotton wool!

matt_drummer

smallblueplanet said:

matt_drummer said:

Reed_Richards said:

matt_drummer said:.

The room temperature is irrelevant.

So no Load Compensation option with Daikin heat pumps?  My LG heat pump will do this, although I hadn't realised until I set it up for a 3rd party controller and that overrides the Load Compensation option.  I keep thinking I should alter the jumper that would enable Load Compensation but I've never quite been brave enough.

Yes, it can load compensate with the Madoka controller, that is Daikins own fancy room thermostat.

The Madoka monitors how quickly the room is heating or cooling and modulates the flow temperature within adjustable parameters to keep a stable room temperature. It does not adjust the dT to do this.

The room temperature is of no relevance to dT though, it isn't on any heat pump.

If I set my heat pump to run at a dT between flow and return of 5c it doesn't matter whether my room is 17c or 23c, you still get a dT of 5c.

I am sure yours is the same?

I'm still confused by what changes the Flow Rate, it must be more than dT? Feel free to correct me as my head feels like it is stuffed with cotton wool!

You set the dT at whatever you like, say 5c.

Then, if you set a flow temperature of say 35c, either by fixed lwt or wdc, then the return temperature is now set at 30c.

The flow rate is adjusted to keep the return at 30c.

If the water comes back cooler than 30c the the flow rate increases and you get more heat and vice versa until you reach the lower and upper limits of the circulation pump.

ninjaef

matt_drummer said:

Another way to think about this is from the point of view of the heat pump.

In two different scenarios producing the same amount of heat it can either heat 10 litres of water a minute by 10c (that is at a dT of 10c) or 20 litres of water a minute by 5c (at a dT of 5c)

Both scenarios result in the same amount of energy being required.

But as the amount of energy consumed by the heat pump is variable, it generates more energy than it consumes by extracting energy from large volumes of air and transferring it to a refrigerant and then the water, it may take more electricity to heat a smaller volume of water by a larger temperature than vice versa.

A dT of 5c is considered by most people to be the optimum. Lower the dT and you have to heat a larger volume of water less, and raise the dT you have to heat a smaller volume of water by a larger amount to get the same result.

There is a point where the best efficiency is achieved which is why Octopus set it to fan coils with a dT of 5c even though you have radiators.

perfect. thanks for that knowledgeable insight. 

smallblueplanet

matt_drummer said:

smallblueplanet said:

matt_drummer said:

Reed_Richards said:

matt_drummer said:.

The room temperature is irrelevant.

So no Load Compensation option with Daikin heat pumps?  My LG heat pump will do this, although I hadn't realised until I set it up for a 3rd party controller and that overrides the Load Compensation option.  I keep thinking I should alter the jumper that would enable Load Compensation but I've never quite been brave enough.

Yes, it can load compensate with the Madoka controller, that is Daikins own fancy room thermostat.

The Madoka monitors how quickly the room is heating or cooling and modulates the flow temperature within adjustable parameters to keep a stable room temperature. It does not adjust the dT to do this.

The room temperature is of no relevance to dT though, it isn't on any heat pump.

If I set my heat pump to run at a dT between flow and return of 5c it doesn't matter whether my room is 17c or 23c, you still get a dT of 5c.

I am sure yours is the same?

I'm still confused by what changes the Flow Rate, it must be more than dT? Feel free to correct me as my head feels like it is stuffed with cotton wool!

You set the dT at whatever you like, say 5c.

Then, if you set a flow temperature of say 35c, either by fixed lwt or wdc, then the return temperature is now set at 30c.

The flow rate is adjusted to keep the return at 30c.

If the water comes back cooler than 30c the the flow rate increases and you get more heat and vice versa until you reach the lower and upper limits of the circulation pump.

Ahhhh thank you, it becomes a little clearer.

matt_drummer

smallblueplanet said:

matt_drummer said:

smallblueplanet said:

matt_drummer said:

Reed_Richards said:

matt_drummer said:.

The room temperature is irrelevant.

So no Load Compensation option with Daikin heat pumps?  My LG heat pump will do this, although I hadn't realised until I set it up for a 3rd party controller and that overrides the Load Compensation option.  I keep thinking I should alter the jumper that would enable Load Compensation but I've never quite been brave enough.

Yes, it can load compensate with the Madoka controller, that is Daikins own fancy room thermostat.

The Madoka monitors how quickly the room is heating or cooling and modulates the flow temperature within adjustable parameters to keep a stable room temperature. It does not adjust the dT to do this.

The room temperature is of no relevance to dT though, it isn't on any heat pump.

If I set my heat pump to run at a dT between flow and return of 5c it doesn't matter whether my room is 17c or 23c, you still get a dT of 5c.

I am sure yours is the same?

I'm still confused by what changes the Flow Rate, it must be more than dT? Feel free to correct me as my head feels like it is stuffed with cotton wool!

You set the dT at whatever you like, say 5c.

Then, if you set a flow temperature of say 35c, either by fixed lwt or wdc, then the return temperature is now set at 30c.

The flow rate is adjusted to keep the return at 30c.

If the water comes back cooler than 30c the the flow rate increases and you get more heat and vice versa until you reach the lower and upper limits of the circulation pump.

Ahhhh thank you, it becomes a little clearer.

Obviously, if you have set a wdc and the outside temperature changes then so does your flow temperature but because the dT is fixed the return temperature follows the flow.

Modulation, overshoots and offsets have an effect on the flow temperature, but as far as I am aware, the return will still follow to maintain the set dT.

However, my experience is that the flow rate varies quite a lot doing this and nothing is very stable.

I don't think it is really an issue but I choose to set radiators and have the lowest flow rate possible as I can never get to a dT of 10c. All that means in reality is that my heat pump never increases the flow rate and it is the only way to get a stable flow rate. 

I think most other heat pumps do this differently and I have learnt today that this a bit old school from the days without inverter driven compressors. Most other heat pumps run at a constant flow rate, Daikin do it differently.

I just find that my way in my house is most efficient and gives the closest to a steady heat output that I can get, and that is what I want.

The heat pump still `hunts' at low flow temperatures but that is how they all seem to be.