Heat Pump Query

[frank]

I've got a ground source heat pump in for repair as one of the plate heat exchangers failed and filled the system with ground water.

The layout of the pipework, which I am having to replace seems a little odd.

If you follow the path of the liquid in each mode (heating and cooling) there appears to be a continuous loop bringing the second TEV in to play? The TEV's are externally equalised but I've left the equalisation line off the drawing for clarity.

Can anyone explain why this layout is made this way? - or is it a mistake?

Only one filter drier seems to be bugging me as well?

Confused?????????

[MikeHolm]

I can guess that they thought one filter would catch everything over time (cheap buggers). I assume it is a one way filter.....

I think only one TEV is active at a time and the not needed branch will inactive due to higher pressures on the other side and the NRV.

How old is it?

[frank]

I can guess that they thought one filter would catch everything over time (cheap buggers). I assume it is a one way filter.....

I think only one TEV is active at a time and the not needed branch will inactive due to higher pressures on the other side and the NRV.

How old is it?

Yes it's a one way filter, and the unit is about 2 years old - rated at 20kW

[al]

Both tev's will be fed but so long as NRV's are functioning then only one will ever be flowing through. looks like a York layout, but my question would be why have a 4 way valve, if ground water is always being cooled?

I've a similar set up here but no 4 way valve, just actuators on the water piping to allow cold water feed fan coils in summer and switch to underfloor heating in winter, river water feeds the unit rather than ground source.

al

[frank]

It's a genuine heat pump...i.e.heating and cooling as per the diagrams. Just cant get my head around why the liquid feeds into both TEV's no matter which mode it is in?

[al]

saves fitting two solenoid valves? as i say the nrv only allows one to function.

al

[MikeHolm]

It actually seems logical to me except for the filter, should be another one. I just looked at a well known groundsource unit here and it also had the same arrangement.

[MikeHolm]

It will only feed in one way at a time so it is like having two complete systems.

[al]

Yep, why would you want to heat the ground water though?

al

[Bigfreeze]

Yep, why would you want to heat the ground water though?

al

The ground water is your heat dump when in cooling mode.

[Bigfreeze]

System looks fine to me and I don't think a second drier would be necessary in such a small system. Wouldn't have more than 3.5kg of refrigerant I'd imagine

[MikeHolm]

There ya go.. the master has spoken.

[install monkey]

similar pipework to marc5180's post regaurding ahu strange pipework.ideally fit another drier feeding the other tev,as 1 tev is prone to clogging as the gauze has a smaller surface area than the drier

[Brian_UK]

It's a genuine heat pump...i.e.heating and cooling as per the diagrams. Just cant get my head around why the liquid feeds into both TEV's no matter which mode it is in?But it doesn't feed liquid into both according to your plan, one has liquid and the other has mixed low pressure as it's on the outlet of the other one.

[install monkey]

but the non return valve downstream will stop the flow, as long as the non return valves seat properly and the 4 way valve is good it will work,honest

[frank]

Gents

Look carefully at the one way valves.

When in heating mode, (top sketch) the liquid exiting the condenser HE bypasses the outlet of the LH TEV, enters the filter drier and then the RH TEV. As it exits this TEV to feed into the evaporator HE, it also feeds back towards the LH TEV and creates a loop of liquid between the TEV's

It's similar when in cooling mode.

The machine feeds a Pre-heat coil/Pre-cooling coil on an AHU

I'm used to seeing the NRV's on a bypass across the TEV, not as shown here

[mad fridgie]

Gents

Look carefully at the one way valves.

When in heating mode, (top sketch) the liquid exiting the condenser HE bypasses the outlet of the LH TEV, enters the filter drier and then the RH TEV. As it exits this TEV to feed into the evaporator HE, it also feeds back towards the LH TEV and creates a loop of liquid between the TEV's

It's similar when in cooling mode.

The machine feeds a Pre-heat coil/Pre-cooling coil on an AHU

I'm used to seeing the NRV's on a bypass across the TEV, not as shown here

look at heating mode

Just look at the TEV feed by the drier. It feeds the right evap. So far so good? What is the pressure at the heat exchanger inlet.?

But I hear you say "but it feed the inlet into the second valve as well". Yes it does, "sort of"
Now what is the pressure at the "outlet" of this second TEV?

So to get flow you in this direction the the pressure must be higher at the inlet of the TEV than that of the outlet!!!.

[Bigfreeze]

Gents

Look carefully at the one way valves.

When in heating mode, (top sketch) the liquid exiting the condenser HE bypasses the outlet of the LH TEV, enters the filter drier and then the RH TEV. As it exits this TEV to feed into the evaporator HE, it also feeds back towards the LH TEV and creates a loop of liquid between the TEV's

It's similar when in cooling mode.

The machine feeds a Pre-heat coil/Pre-cooling coil on an AHU

I'm used to seeing the NRV's on a bypass across the TEV, not as shown here

Print off your sketch. Then draw in the pressures you would expect to see at each point in the system in heating mode on the first sketch and cooling on the second sketch. That should sort it out in your head as to how the system should operate, although totally dependent on the quality of the NRV's used.

[chemi-cool]

Frank, is the HP feeds an AHU? Cause if it does, then its all clear, heatind mode and cooling mode.
With GSHP you can easily cool during cold winter, server rooms for instance.

one drier is doing the job perfect as all the liquid circulate through it, in cooling mode, there is no back flow cause of the NRV before the TXV.

[frank]

OK ...I hear the arguments regarding pressures but it's the NRV's that are causing me difficulties.

Look at the attached sketch with liquid flow arrows on and explain why they are there?

[mad fridgie]

If the NRV were not there the high pressure liquid would back through the expansion valves without any control.
The non operating TEV would be fully open as the bulb is effectively connected to the discharge line.

[chemi-cool]

Ok Frank, its all about differences in the refrigerant pressure in the different modes,

To ease my explanation, I will give the NRV on the left 1 and the TXV that's follow it 1 as well.

In heating mode, the pressure entering NRV 1 is high pressure and pressure entering the other NRV is low.
Therefore it will remain closed when unit is in heating mode.
In cooling mode it exactly the opposite.

[MikeHolm]

There is a higher pressure at the output tee at TEV1 than at the output of TEV2 during heating so, to me, regardless of whether the TEV is open on not, the flow will go to the EVAP.

When i was learning fluid flow (and electrical flow) years ago, i would picture myself as a bit of liquid or gas flowing through a pipe and watch as the stream hit different obstacles and tributaries. I don't know if anyone else looked at it that way but it worked for me rather well.

[chemi-cool]

When i was learning fluid flow (and electrical flow) years ago, i would picture myself as a bit of liquid or gas flowing through a pipe and watch as the stream hit different obstacles and tributaries. I don't know if anyone else looked at it that way but it worked for me rather well.

I bet you thought you were a drop of R-12. Mind you, it is prety dark inside the system apart from the sight glass....:D

[frank]

The NRV's are not dependant on pressure drop, only direction of flow.

As the flow through these NRV's does not change in either heat or cool mode, why are they in circuit?

[MikeHolm]

If an NRV has 5 bar on the upstream side and 1 bar on the downstream side, you would not get flow until the pressures equalized (plus the resistance of the mechanism). NRV 1 is only active (ie; blocking flow) in cooling mode and NRV 2 is only active in heating mode so there cannot be a working circuit without them (IMHO).

[MikeHolm]

I bet you thought you were a drop of R-12. Mind you, it is prety dark inside the system apart from the sight glass....:D

Actually I was a drop of propylene glycol lying on a raft of sediment

[Peter_1]

I agree with Frank, the NRV's are not positioned the right way. There was a better solution in IMHO, something like we did it on a HP we made in a truck (see attachment)

[install monkey]

wow-4 mods commenting on 1 thread within 28 replies- sorry- it will work in both modes but as you say it could be piped better

[MikeHolm]

The first one is very simple and workable. I would be interested to know, Peter, why the second one would work better?

[frank]

The first one is very simple and workable. I would be interested to know, Peter, why the second one would work better?
In the first layout Mike, each NRV only ever has liquid flowing in 1 direction in either mode i.e. they are never subject to reverse flow.

In the conventional setup as Peter's photo shows, (and the attached pdf) the NRV's are subject to reverse liquid flow and so have their place in the circuit.

My original post asks why the NRV's are in circuit when they are never subject to reverse flow?

I could not see the point of re-piping the heat pump we have in for repair in this way.

[mad fridgie]

yes they are, subject to reverse pressure, neither or subject to reverse flow, they are there to stop flow, so no reverse flow occurs, both have reverse pressure, stopping reverse flow. you are assuming that the TEV is acting as a NVR, 'IT IS NOT'
Peter drawing show a receiver, which allows for the variant in refrigerant flow, and heat transfer properties in each cycle

[Peter_1]

Just to have no confusion: in the receiver, both pipes are going to the bottom of the tube, tubes cut off under 45°. Reason why we made one ourselves, I couldn't find quick the right one we then needed.
The two receivers on the background are 'normal' receivers, flow in one direction and therefore mounted inclined/sloped
And we were still busy with the install when I made the pictures ;-)

[MikeHolm]

OK, in Franks drawing the circuit is VERY simple and you have only one flow direction at any one time because the NRVs stop the unwanted flow. In Peters system, the only difference i see is the small Receiver (can you make a drawing like Franks?) as i don't see where the larger receivers are connected.

[chemi-cool]

frank, your last drawing will not work as the TXV will transfer liquid\gas in both directions.

[Yuri B.]

In the first variant there is a lack of the filter for cooling mode.
In the latter, the shared filter will discharge crap it may accumulate during another mode.

[Peter_1]

frank, your last drawing will not work as the TXV will transfer liquid\gas in both directions.
I disagree Chemi. Both NRV's are mounted in opposite directon and there will be always 1 NRV which will block the liquid flow, whatever the direction may be.
The only additional item we have is a liquid receiver where Frank has drawn his filter/drier.
.

[chemi-cool]

I disagree Chemi. Both NRV's are mounted in opposite directon and there will be always 1 NRV which will block the liquid flow, whatever the direction may be.
The only additional item we have is a liquid receiver where Frank has drawn his filter/drier.
.

I was referring to Frank's last drawing.