ASHP - how noisy are they in reality

[SteamyTea]

@Beau

If your water pump built into the ASHP or separate?

If a separate one, can it be adjusted easily?

 

[Beau]

28 minutes ago, SteamyTea said:

@Beau

If your water pump built into the ASHP or separate?

If a separate one, can it be adjusted easily?

 

It's built into the heat pump. According to the specs flow rates go from 540-1205 l/h. My gut feeling listening to it is it operates at one or the other and doesn't modulate between the two.

[SteamyTea]

8 minutes ago, Beau said:

It's built into the heat pump. According to the specs flow rates go from 540-1205 l/h. My gut feeling listening to it is it operates at one or the other and doesn't modulate between the two.

I may be teaching grandmother to suck eggs, but is there something in the controller to set it?  It may be under installer settings, rather than user settings.

[Beau]

30 minutes ago, SteamyTea said:

I may be teaching grandmother to suck eggs, but is there something in the controller to set it?  It may be under installer settings, rather than user settings.

Not at all. I was very familiar with our old GSHP but haven't really got my head around this ASHP and its controls

 

There are two controllers. One is now built into a cupboard as I was told I wouldn't need to touch it once up and running and the other does have an installer level section but I cant see anything about flow rates on it.

[SteamyTea]

2 minutes ago, Beau said:

One is now built into a cupboard as I was told I wouldn't need to touch it once up and running

That will be the one to fiddle with.  Is it really hard to get to and read.

[John Carroll]

One might think that, assuming a modulating as against a on/off ASHP,  that the pump should be automatically controlled to give maybe a fixed dP of say 5C, the flowrates above of max/min of 540/1205 LPH would then give  a ASHP output of 3.14/7.0 kW.

[Nickfromwales]

1 hour ago, Beau said:

It's built into the heat pump. According to the specs flow rates go from 540-1205 l/h. My gut feeling listening to it is it operates at one or the other and doesn't modulate between the two.

The pump should be PWM and be controlled by the heat pump to match duty.

 

It should come on at higher output when the return temp is low, and start to dial down as demand gets lower / return temp increases.

 

I know that with Stiebel Eltron (external pump and controls) you need to set this during commissioning. One we installed hadn’t been commissioned properly (agent missed a setting by mistake) and this meant the main circulation pump was just going flat out; this didn’t allow an opportunity for any heat to amass and then the HP locked out after 10 mins or so (assuming compressor failure).

 

I’m not familiar with all HP’s (so just FYI) so you can ask the question.  

[marshian]

1 hour ago, Beau said:

It's built into the heat pump. According to the specs flow rates go from 540-1205 l/h. My gut feeling listening to it is it operates at one or the other and doesn't modulate between the two.

 

 

How many rads?

Heat loss of the house?

 

Just for comparison and I know it's never going to be a valid comparison but 4 Bed Detached, 2 floors, 113m3 (stupid T shape so a bunch of rooms have 3 external walls) 13 Rads, circuit volume 130 L, Heat Loss 4.74 kWh - Pump Flow rate is between 300 and 600 L/Hr (former being heating circuit which has a lot more restriction and later being when on HW cyl reheat)

[JamesPa]

3 hours ago, John Carroll said:

One might think that, assuming a modulating as against a on/off ASHP,  that the pump should be automatically controlled to give maybe a fixed dP of say 5C, the flowrates above of max/min of 540/1205 LPH would then give  a ASHP output of 3.14/7.0 kW.

From discussions on another forum different ASHPs do different things.  eg Vaillant has a PWM pump which it adjusts down at installation time to match its max output @ approx DT5, then leaves constant.  There is also the possibility to manually adjust in the installer menu.  Samsung, if you fit a PWM pump, apparently adjusts to constant DT depending on load, but with a floor rate.  Daikin does something different still.   Mitsubishi is constant speed I am told, although it does support a pwm pump so maybe same as Vaillant.

 

The question, to which I have yet to find a satisfactory answer, is whats best for efficiency and/or is that itself heat pump dependent.  Pure Carnot thermodynamics would argue that low emitter DT = higher average emitter temperature for any given flow temperature = better COP, so make DT as low as possible (consistent with noise, pipe erosion etc).  The folks on openenergymonitor trade this equation off against water pump consumption to get an 'optimum', which is fair enough.  Some others argue that there are compressor related factors which aren't just the Caront equation, however they arent specific and until they are the argument has only limited credibility.  If anyone has a 'chapter and verse' on this with the physical principles on which the argument is based id be interested!

Edited Friday at 11:24 by JamesPa

[SteamyTea]

4 minutes ago, JamesPa said:

The question, to which I have yet to find a satisfactory answer, is whats best for efficiency and/or is that itself heat pump dependent

I think it can only be compared to the idealised Carnot cycle because, as you say, different systems use different control.

[SteamyTea]

Had a while to kill, so had a think about efficiency of heat pumps.

 

Basically there are 3 variables, Power, Temperature in the cold side and Temperature on the hot side.

These should fit a curve that follows 1-√(T_c/T_h) for efficiency at maximum power.

 

 

I have used a simple scale, 0 is nothing, 1 is everything.

Because this is a heat pump, the y-axis can be scaled to represent CoP.

 

To establish the true efficiency of a heat pump, data really needs to be collected for OAT, IAT and flow rates (both air/water and delivery depending on setup).

[Alan Ambrose]

>>> Pure Carnot thermodynamics

 

I haven't heard that word for .... 40 years since engineering school  Knew it would come in useful one day - well it would if I could remember what it was about.

[SteamyTea]

4 minutes ago, Alan Ambrose said:

remember what it was about

The theoretical, maximum, efficient from a heat engine.

Heat is the old word for energy, so can be used in some non thermal applications.

 

More applicable to thermal applications though. I was also thinking about why ICE engines are so rubbish while wondering about all this thermodynamics.

[John Carroll]

The closer the evaporating and condensing temperatures are, the less compressor power required, a very quick look at 410A refrigerant tables shows, purely based on the table pressures,  ~ a pressure ratio of 3.148 in compressing from -5C to 35C and 3.727 in compressing from -10C to 35C so ~ 18/19% more power required maybe?

[Beau]

22 hours ago, marshian said:

 

 

How many rads?

Heat loss of the house?

 

Just for comparison and I know it's never going to be a valid comparison but 4 Bed Detached, 2 floors, 113m3 (stupid T shape so a bunch of rooms have 3 external walls) 13 Rads, circuit volume 130 L, Heat Loss 4.74 kWh - Pump Flow rate is between 300 and 600 L/Hr (former being heating circuit which has a lot more restriction and later being when on HW cyl reheat)

Thanks. I will try and dig out the details 

[LnP]

18 hours ago, SteamyTea said:

Heat is the old word for energy, so can be used in some non thermal applications.

Actually not correct. Second law of thermodynamics, there are two types of energy, heat and work. Work can be converted completely into heat; but heat cannot be converted completely into work, the best you can theoretically achieve is a Carnot heat engine.

Fossil fuels provide heat energy and electricity provides work energy.

The second law is not well understood but important in the context of plotting a course to net zero. 

Edited Saturday at 11:29 by LnP

[JamesPa]

7 minutes ago, LnP said:

The second law is not well understood but important in the context of plotting a course to net zero. 

I never much liked the second law, it should be repealed in my view.  Perhaps The Donald can organise this for us.

[SteamyTea]

15 minutes ago, LnP said:

there are two types of energy, heat and work

So work is not the rate at which heat is used then?

[JamesPa]

2 minutes ago, SteamyTea said:

So work is not the rate at which heat is used then?

There is a description here

[LnP]

5 hours ago, SteamyTea said:

So work is not the rate at which heat is used then?

No. Heat and work are the two different types of energy, measured in Joules. Power is the rate of doing work measured in Joules per second. A J/s is a Watt.

 

The first law (conservation of energy) is easy. The second law is tricky. Politicians don’t understand it which is one reason why we get incoherent energy policies.

[JohnMo]

2 minutes ago, LnP said:

Politicians don’t understand it which is one reason why we get incoherent energy policies

Sorry that is just nonsense.  Don't think any understanding of thermodynamics is required to get a coherent energy policies. Certainly don't think a working knowledge of Enthalpy is a prerequisite, for any politician or even their advisor.

[SteamyTea]

2 hours ago, LnP said:

No. Heat and work are the two different types of energy, measured in Joules. Power is the rate of doing work measured in Joules per second. A J/s is a Watt.

That is like saying that distance and speed are the same thing.

[LnP]

3 hours ago, JohnMo said:

Sorry that is just nonsense.  Don't think any understanding of thermodynamics is required to get a coherent energy policies. Certainly don't think a working knowledge of Enthalpy is a prerequisite, for any politician or even their advisor.

I don't understand your point about enthalpy. Did you mean entropy? Either way, there are different ways to state the second law. I tried to make it simple and deliberately didn't bring entropy into it. I just saw something which was incorrect, is a common misconception and incorrect in a way which sometimes leads to poor energy policy making. So I hoped to straighten that out.

 

A political example ... if our politicians understood this science better, they wouldn't be wasting tax payers' money on subsidising projects which use hydrogen as an energy vector, for example this one in Aberdeen, especially given that in Montpellier they already learned the hard way.

Compare:

Renewable electricity -> hydrogen (heat energy) via an electrolyser -> electricity via a fuel cell -> work energy via an electric motor .... or -> work energy via hydrogen internal combustion engine.

Versus:

Renewable electricity -> work energy via an electric motor in a BEV.

 

Apologies if this has hijacked the thread!

[LnP]

1 hour ago, SteamyTea said:

That is like saying that distance and speed are the same thing.

Power is to work as speed is to distance 🙂. One is the rate of the other.

[JohnMo]

26 minutes ago, LnP said:

Renewable electricity -> hydrogen (heat energy) via an electrolyser -> electricity via a fuel cell -> work energy via an electric motor .... or -> work energy via hydrogen internal combustion engine.

Versus:

Renewable electricity -> work energy via an electric motor in a BEV.

Also sorry for hijack

 

That arguement is sound BUT, if the wind turbine or whole wind farm is being physically switched off and the wind farm being paid to do so (as happens quite regularly), then renewable to hydrogen makes perfect sense. It's excess electricity being stored instead of having been switched off. Hydro storage is part of that mix also.

 

The BEV makes sense also, but if wind power is being switched off even when the BEV is charging, hydro storage is being pump up the hill, hydrogen makes sense.