Heat Pump setting with buffer tank

[Wingover]

Hi All,

 

need some help understanding the best configuration of the air to water heat pump.  I currently have an LG Threma V outdoor unit connected to domestic hot water tank and a buffer tank for the UFH.  When running in the UFH mode the unit is set for 36c temp but my buffer tank (built in) temp dial shows 30c all the time.

 

I am wondering if it is best to set up the outdoor unit to run on Delta T (7c) pump setting or continuous flow?  Do you also setup the control to look at outlet temp or inlet temp?

[IanR]

23 minutes ago, Wingover said:

but my buffer tank (built in) temp dial shows 30c all the time.

 

Is it a 4 port buffer? What size is it? What height is the temp sensor?

 

Assuming 4 port (or 3 port) I'd go with flow temp control running off a weather compensation curve.

[Wingover]

9 minutes ago, IanR said:

 

Is it a 4 port buffer? What size is it? What height is the temp sensor?

 

Assuming 4 port (or 3 port) I'd go with flow temp control running off a weather compensation curve.

 

Thanks for the reply.  Yes, 4 port 100L tank the plastic temp dial is about 2/3 up from the bottom.

When you say flow temp, do you mean inlet or outlet temp control? I did setup a weather compensation curve.

[JohnMo]

Do you also have a mixer valve and pump on the UFH?

[Wingover]

5 minutes ago, JohnMo said:

Do you also have a mixer valve and pump on the UFH?

No mixing valve.  Just a (spring) bypass between in and out after the pump.  Pump has 3 speed settings on it.  I was told I don't need a mixing valve as I run "low" temp heat pump since there are no radiators.

[JohnMo]

If you run with all open loops (no room thermostats - all on or all off), you could just bypass and remove the buffer and the second pump. If you want need room thermostats, keep the buffer. The thing with buffers is both the primary and secondary flow rates need to be balanced otherwise you get mixing in the buffer which isn't good, that is maybe why you are seeing different temps to what you expect.

 

I would if with buffer, run straight WC, keep as many zones open as possible all the time, ideally all of them and balance flow rates on the UFH.  More flow warmer room, lower flow for a cooler room. Balance the flow rates on both pumps

 

 

[Wingover]

3 minutes ago, JohnMo said:

If you run with all open loops (no room thermostats - all on or all off), you could just bypass and remove the buffer and the second pump. If you want need room thermostats, keep the buffer. The thing with buffers is both the primary and secondary flow rates need to be balanced otherwise you get mixing in the buffer which isn't good, that is maybe why you are seeing different temps to what you expect.

 

I would if with buffer, run straight WC, keep as many zones open as possible all the time, ideally all of them and balance flow rates on the UFH.  More flow warmer room, lower flow for a cooler room. Balance the flow rates on both pumps

 

 

I have two manifolds (two floors) with 8 zones each.  I have thermostats in each room and I adjusted the flow for each loop.

Can you explain a bit regarding the primary and secondary flow rates?  Do you mean the heat pump own water pump and the pump I have after the buffer tank? How do you go about that?

 

Here is a picture of the tank (and orange) pump.

[IanR]

46 minutes ago, Wingover said:

Thanks for the reply.  Yes, 4 port 100L tank the plastic temp dial is about 2/3 up from the bottom.

When you say flow temp, do you mean inlet or outlet temp control? I did setup a weather compensation curve.

 

Keep an eye on the temp gauge, there's no circumstance where it should stay at 30°C. At 2/3 up the tank then when the ASHP is on it should mostly be showing a temp around the flow temp, and when the ASHP switches off, if the UFH is still running it will, after a while, drop to return temp, shortly before the ASHP switches back on.

 

Flow temp is water temp coming away from the ASHP.

 

14 minutes ago, Wingover said:

Can you explain a bit regarding the primary and secondary flow rates?  Do you mean the heat pump own water pump and the pump I have after the buffer tank? How do you go about that?

 

The flow rates either side of the buffer do not need to balance, a 4 port buffer is there to allow the exact opposite, ie, the UFH to take energy from the buffer at a different rate to what the ASHP supplies it, it's what protects the system from short cycling.
 

14 minutes ago, Wingover said:

 

The biggest improvement you could make is some insulation on those pipes.

Edited November 1 by IanR

[Wingover]

14 minutes ago, IanR said:

 

Keep an eye on the temp gauge, there's no circumstance where it should stay at 30°C. At 2/3 up the tank then when the ASHP is on it should mostly be showing a temp around the flow temp.

 

 

and when the ASHP switches off, if the UFH is still running it will, after a while, drop to return temp.

 

Unfortunately, it doesn't seem to be the case.  I noticed that if the flow is at 35c the tank shows a bit less (maybe 30c)

 

Yes, that does happen.

Edited November 1 by Wingover

[IanR]

3 minutes ago, Wingover said:

 I noticed that if the flow is at 35c the tank shows a bit less (maybe 30c)

 

You'll be losing a lot of temp from the uninsulated pipe work. Can you measure the temp on the pipe into the buffer from the ASHP, just at the joint to the tank.

[Wingover]

3 minutes ago, IanR said:

 

You'll be losing a lot of temp from the uninsulated pipe work. Can you measure the temp on the pipe into the buffer from the ASHP, just at the joint to the tank.

Sure.  It is off right now but later today I will.  I will get some insulation as well.  Didn't think you lose much since it is inside the house.

[JohnMo]

56 minutes ago, IanR said:

The flow rates either side of the buffer do not need to balance, a 4 port buffer is there to allow the exact opposite,

Sorry - if flow rates are different you get mixing, if flow rates are the same or close, you get a thermocline form. With different flow rates that thermocline doesn't occur. So you get inefficiency as return temp to ASHP gets distorted and is higher than it needs to be.

[JohnMo]

41 minutes ago, Wingover said:

Didn't think you lose much since it is inside the house

Agreed, for heating system, but cylinder pipes from diverter valve need to be insulated and primary pipes from heat pump to diverter valve need insulation, and DHW piping.

[Wingover]

2 minutes ago, JohnMo said:

Sorry - if flow rates are different you get mixing, if flow rates are the same or close, you get a thermocline form. With different flow rates that thermocline doesn't occur. So you get inefficiency as return temp to ASHP gets distorted and is higher than it needs to be.

How do you control that? Since some rooms are off and the pump starts pushing water back through the balancing valve (on top in the picture from before)?

[JohnMo]

3 minutes ago, Wingover said:

How do you control that? 

It happens when you have lots of zones. Control by either less zones, have the zones open longer by reducing the need for the thermostat to react by reducing flow temp or flow rate or both.

 

My UFH system went from thermostat in every room, big buffer, multiple pumps, to no thermostat, no buffer and one pump. More efficient, more stable room temps. 

[IanR]

8 minutes ago, JohnMo said:

Sorry - if flow rates are different you get mixing, if flow rates are the same or close, you get a thermocline form. With different flow rates that thermocline doesn't occur. So you get inefficiency as return temp to ASHP gets distorted and is higher than it needs to be.

 

That's not correct. A 4P buffer is to allow hydraulic separation, allowing the emitter circuit to take energy at a different/slower rate than the ASHP adds energy, reducing short cycling. Thermocline/stratification is a robust phenomena that does not require balanced flow rates - it occurs in HWCs that do not have balanced flow rates, and have no baffles or features to promote stratification.

[Wingover]

16 minutes ago, IanR said:

 

That's not correct. A 4P buffer is to allow hydraulic separation, allowing the emitter circuit to take energy at a different/slower rate than the ASHP adds energy, reducing short cycling. Thermocline/stratification is a robust phenomena that does not require balanced flow rates - it occurs in HWCs that do not have balanced flow rates, and have no baffles or features to promote stratification.

I checked the temps at the buffer tank but all zones were closed (pump still runs) I get 35C or very close to it in all 4 ports.  I will check it again when all zones are open and the heat pump has to work hard.

[JohnMo]

1 hour ago, Wingover said:

I checked the temps at the buffer tank but all zones were closed (pump still runs) I get 35C or very close to it in all 4 ports.  I will check it again when all zones are open and the heat pump has to work hard.

So the thermocline is obviously not that robust. Contrary to what you state below.

 

1 hour ago, IanR said:

Thermocline/stratification is a robust phenomena that does not require balanced flow rates

 

1 hour ago, IanR said:

4P buffer is to allow hydraulic separation, allowing the emitter circuit to take energy at a different/slower rate than the ASHP adds energy, reducing short cycling.

Do not disagree - but also doesn't mean it's efficient. You can actually end up with the heat pump cycling to keep the buffer happy and provide zero energy to the house.

 

[IanR]

4 minutes ago, JohnMo said:

So the thermocline is obviously not that robust. Contrary to what you state below.

 

? The emitters are not on, the Buffer is at flow temp, possibly fully charged. You can't draw any conclusions, unless you have a biased view.

 

6 minutes ago, JohnMo said:

Do not disagree - but also doesn't mean it's efficient. 

 

A 4P buffer removes the inefficiencies and warranty concerns of short cycling, at the cost of minor standing losses and powering a second circulation pump that would not otherwise be required in most cases.
 

9 minutes ago, JohnMo said:

You can actually end up with the heat pump cycling to keep the buffer happy and provide zero energy to the house.

 

? The ASHP will switch off when the buffer is fully charged at flow temp.

[Wingover]

19 hours ago, IanR said:

 

? The emitters are not on, the Buffer is at flow temp, possibly fully charged. You can't draw any conclusions, unless you have a biased view.

 

 

A 4P buffer removes the inefficiencies and warranty concerns of short cycling, at the cost of minor standing losses and powering a second circulation pump that would not otherwise be required in most cases.
 

 

? The ASHP will switch off when the buffer is fully charged at flow temp.

So I checked when the system was running and here is a picture with the temps next to each port.  I guess the incoming temp is not going directly to the floor manifold 

[dpmiller]

how are you measuring the pipe temps?

[Wingover]

16 minutes ago, dpmiller said:

how are you measuring the pipe temps?

with a laser gun

[dpmiller]

can't trust the numbers then as the shiny surface is innacurate. Wrap some tape of some kind around the pipe wherever you're pointing the gun...

[IanR]

3 hours ago, Wingover said:

So I checked when the system was running and here is a picture with the temps next to each port.  I guess the incoming temp is not going directly to the floor manifold 

 

The gauge in the pocket 2/3 up looks close to me measuring at 35°C, although both the gauge and the laser temp gun will likely have a ±1°C tolerance so can't be relied on to compare between the two. You'll need to measure a few times to get a feel for what is going on, the temps are dynamic as the ASHP comes on and off and you're wanting 0.1° accuracy which isn't achievable with consumer devices. It would be nicer to see the temps across the top, and those at the bottom within 1° of each other. If after multiple readings, at different times, you are still seeing a similar result are you could try to slow the emitter pump down and are you able to limit the flow rate of the ASHP? Not sure if it's a setting available on all HPs, but I can turn mine down (on space heating only) to make it run slower for longer.

 

I set mine up with a data logger and DS18B20 sensors and some times the traces would show the flow temp to the emitters higher than the flow from the ASHP, which isn't possible - the accuracy of the readings I need are not within the capability of the DS18B20's. After about 10 different sets of readings, each running for a couple of hours mine averaged out with the emitter side being within 0.5°C of the ASHP, except just as the ASHP stopped or started.

 

Is it cold enough that the emitter circuit is running continuously (my own heating isn't on yet), are the measurements you have taken are at a reasonably steady state?

Edited November 2 by IanR

[Wingover]

The picture is from a different time I just used it to put the temps on so you can see.  The plastic gauge showed 31c when I took the measurements.

 

It is not as cold so I will wait until all zones are on and take several measurements at that time.

I can choose on the ASHP to run it's own pump (not the one by the buffer tank) on several different modes.

1. Delta T

2. Automatic flow 

3. Capacity adjustment from 10% to 100%