Interested in a Heat Pump...

[siletto]

31 minutes ago, joth said:

Sort of. You only need an "adequate" installation to achieve COP of 3, I'd say the nuance here is that the typical UK installation in below adequate.

 

What makes "adequate" an install in your terms? 

 

[PhilT]

2 hours ago, Alan Ambrose said:

 

Is the logic here 'electricity is 3x price per kW than gas, so you need an average CoP > 3 (to swap out a gas boiler for a HP) and you'll only get that with a very good HP install'?

This user monitor is quite encouraging. Things have definitely improved, but the usual caveats still apply. https://heatpumpmonitor.org/

[sharpener]

9 minutes ago, siletto said:

What makes "adequate" an install in your terms? 

 

For starters:

• Well matched to the heating and hot water requirements of the house and its occupants
• Not over-specified or unnecessarily complicated
• Installed in accordance with manufacturers' recommendations
• Proper frost protection and lagging
• Set up correctly to achieve best attainable performance
• Controls that are fit for purpose, easy to use and properly explained to the customer

Edited December 7, 2023 by sharpener

[joth]

1 hour ago, sharpener said:

For starters:

• Well matched to the heating and hot water requirements of the house and its occupants
• Not over-specified or unnecessarily complicated
• Installed in accordance with manufacturers' recommendations
• Proper frost protection and lagging
• Set up correctly to achieve best attainable performance
• Controls that are fit for purpose, easy to use and properly explained to the customer

 

Great list. 

For me "Installed in accordance with manufacturers' recommendations" is a key one. I had to put so much right on mine just to make it match the MIs. And of course meeting building code and the MCS guidelines should get a mention here too.

 

"Set up correctly to achieve best attainable performance" I think is perhaps asking a bit much. Best practicably attainable maybe more like it. It's uneconomic and unrealistic for an installer to chase diminishing returns by squeezing out every last possible saving. That's like expecting a service in the local garage to race-ready tune your car. What's important is to avoid egregious design or commissioning errors. It's far too typical for installs to have short cycling, setup with very high flow temps, no weather compensation, or oversized buffers, any of which can kill performance and the COP>3 goal. (Many these do however avoid maintenance call outs, which lets be honest is why it happens)

 

[JohnMo]

Think the best way to install a heat pump or boiler is as simply as possible.

No zones, no buffer, limited interaction with thermostats, design for sub 35 degs for most the year, set to WC and leave it manage itself.

 

In real life zones are required for many, if more than two zones and/or coupled with a mixer valve, you need a buffer, as the mixer valve or a zone can close.

 

If you need a buffer, install either in flow, return or across flow and return, as a glorified min flow loop with capacity to help mitigate short cycling.

 

When a 4 port buffer is used, it is really important to design well, have good internal design to promote stratification and flow either side of the buffer be balanced to prevent mixing.

 

35 deg flow temp, should achieve a CoP of 3 at zero and about 5.25 at 12 degs. Most the winter is nearer 7 than 0, so if flowing at 35 that should give a CoP 4.5, if you can flow at 30 a CoP over 5.

 

But we all make things more complex than they need to be, mostly at the negative impact to CoP.

 

 

[Beelbeebub]

 

2 hours ago, JohnMo said:

When a 4 port buffer is used, it is really important to design well, have good internal design to promote stratification and flow either side of the buffer be balanced to prevent mixing.

I think this is important.

 

I think historically alot of installations have defaulted to a large 4 port buffer to prevent the installer having to think too hard about the rest of the system.

 

Whilst it does allow the HP to run even if you balls up the other side of the system the cost is the system will run inefficiently in all but perfectly balanced conditions - and if you can achieve those regularly, why bother with a buffer?

 

[JohnMo]

28 minutes ago, Beelbeebub said:

and if you can achieve those regularly, why bother with a buffer?

My lessons learned about buffers

 

People want zones, they think (or have been told) its the good thing to do or have a mixed system with different flow or temperature requirements. The more things you add the more important the buffer becomes.

 

Operated my system without a buffer, but fully open on WC. But one part of the system really needed a different temperature and different running regime. So added a buffer for two different things.

 

UFH in house required a mixer so I could operate at lower flow temperature, chose an ESBE mixer, this stays fully open until set point is reached, then closes to almost fully closed, killing forward flow from HP.

 

The other reason is a small zone of 2x 50m loops can operate on its own if required.

[SteamyTea]

11 hours ago, JohnMo said:

People want zones, they think (or have been told) its the good thing to do

Yes, but I think a lot of that is down to the UK having oversized, but highly modulating, gas boilers.

 

To run less controlled zones relies, more and more, on a decent room by room heat loss calculation.

This becomes harder with UFH as you can only change the flow rate and flow temperature, you can't change the size of the emitter.

 

[JohnMo]

19 minutes ago, SteamyTea said:

This becomes harder with UFH as you can only change the flow rate and flow temperature, you can't change the size of the emitter.

At the design stage you can size the emitter by changing how much pipe is in a room and its spacing, so some room could have 300mm, 200mm, 150mm spacing others 100mm if required, same way as you do radiator sizing based on room heat loss. So then the output could be varied house wide by increasing flow temperature only up or down.

 

Programs like LoopCad have this capability when you design the UFH array.  It tell you how much over or under the room is being heated compared to design requirements.

 

Companies providing design a service never show this on the drawing, because they just pick 150mm centres and fill every space they can with pipe. They are selling product not a design. That's why you see floor plans with with 100s of meters of loops in hallways, when in must cases, next to nothing is required.

[Beelbeebub]

Is there much of a downside to having too much UFH pipe?  

 

The capital cost is fairly negligible.

 

 

[SteamyTea]

36 minutes ago, Beelbeebub said:

Is there much of a downside to having too much UFH pipe

I have been pondering that as well.

 

[joth]

48 minutes ago, Beelbeebub said:

Is there much of a downside to having too much UFH pipe?  

 

The capital cost is fairly negligible.

 

 

More water in the system means a bit more glycol needed, if using it. And maybe slightly longer response times (more water to heat, but offset by less screed)

Both pretty negligible in grand scheme 

Edited December 8, 2023 by joth

[JohnMo]

47 minutes ago, Beelbeebub said:

Is there much of a downside to having too much UFH pipe?  

 

The capital cost is fairly negligible.

 

 

Low cost, but do you then need a thermostat in every room to control the system and individual heat output. Having a couple of long loops in an internal hallway, ends up being very warm. You can only change output so much with flow control alone.

[Beelbeebub]

1 hour ago, joth said:

More water in the system means a bit more glycol needed, if using it. And maybe slightly longer response times (more water to heat, but offset by less screed)

Both pretty negligible in grand scheme 

but also more water volume for defrost so less need for a volumiser!

[SteamyTea]

1 hour ago, Beelbeebub said:

less need for a volumiser

The buffer/volumiser side is something that crossed my mind as well.

 

How sensible is it to run a heat pump (or any 'boiler') very close to the minimum volume.

My feeling is that it is a bit like running a car at the lowest oil, or coolant, levels.  Possible, but probably not really the best thing to do if you can add a bit more easily.

 

[JohnMo]

Smaller the volume the shorter the cycle times. 8 degs here at the moment, I have 2x 50m loops and 50L volumiser/buffer, and almost nothing going in the house floor (mixer valve almost closed), cycle time is around 10 to 15 mins on-off. Last night with house floor engaged (an additional 6-700m of pipe) had a 5 hours run without stopping.

[Beelbeebub]

1 hour ago, SteamyTea said:

The buffer/volumiser side is something that crossed my mind as well.

 

How sensible is it to run a heat pump (or any 'boiler') very close to the minimum volume.

My feeling is that it is a bit like running a car at the lowest oil, or coolant, levels.  Possible, but probably not really the best thing to do if you can add a bit more easily.

 

Agreed, but I don't think the minimum volumes are as high as people think.  Irrc grant/Chofu are happy with a 30l volumizer regardless of the size of the rest of the system, which implies the min volume is around 30-40l.

 

15mm UFH pipe laid at 200mm centers is about ½liter per m2

 

So a small house with a 60m² footprint and UFH only on the ground floor would be nearly 30l before you look at upstairs rads, primary pipework etc.

 

Unless it's a very thin system, UFH adds considerable thermal mass as well

[JohnMo]

1 hour ago, Beelbeebub said:

So a small house with a 60m² footprint and UFH only on the ground floor would be nearly 30l before you look at upstairs rads, primary pipework etc.

Maybe, maybe not, if you add a mixer to the UFH your engaged water volume could very low as the mixer valve isn't always open. Volume and flow rate are important, all heat pumps come with a minimum flow rate requirement, having 8 open loops of pipe behind a mixer valve is meaningless as the mixer comprises both volume available to the HP and flow rate the heat pump can deliver.

 

To have no buffer or volumiser the system needs to be fully open.

[Beelbeebub]

17 minutes ago, JohnMo said:

Maybe, maybe not, if you add a mixer to the UFH your engaged water volume could very low as the mixer valve isn't always open. Volume and flow rate are important, all heat pumps come with a minimum flow rate requirement, having 8 open loops of pipe behind a mixer valve is meaningless as the mixer comprises both volume available to the HP and flow rate the heat pump can deliver.

 

To have no buffer or volumiser the system needs to be fully open.

Yes, you would need a direct UFH mainfold without the mixer and pump or at least a minimum sized always on zone

[Beelbeebub]

I'e be really interested if it was possible for HPs to time multiplex output temps for two zones (UFH and rads).

 

If the system simply switched output temps setpoints in synchronization with a 3port (or 2x 2port) valves that diverted between the two zones I don't see a technical reason why it wouldn't be possible efficiently.

 

I also wonder if you could do defrost cycles by switching to DHW coil. As long as you had a bottom biased coil, you would steal a few degrees from the probably already cold bit of the dhw tank. You would then replenish the heat as the last part of the defrost cycle as you rampee back up to temp.

[SteamyTea]

4 minutes ago, Beelbeebub said:

or at least a minimum sized always on zone

That goes back to the old central heating method of always having the small bathroom radiator on, regardless of what the rest of the radiators were up to.

Then put the thermostat in the coldest, unheated corridor.

 

The problem with not zoning is that you can easily have uneven temperatures.  Take my house, the rear is NE facing, so cold, front is SW facing, so warmer.

Add in afternoon solar gain, even on a day like today, and the front can get quite comfortable while the rear is cold.

2 minutes ago, Beelbeebub said:

I'e be really interested if it was possible for HPs to time multiplex output temps for two zones (UFH and rads).

That crossed my mind as well.

Could do it on just times,  say 40 minutes downstairs and 20 upstairs.  Just a valve on a timer then.

[JohnMo]

22 minutes ago, Beelbeebub said:

or at least a minimum sized always on zone

That misses the point I never really realised, if said zone is behind a mixer it doesn't count.

 

16 minutes ago, Beelbeebub said:

I'e be really interested if it was possible for HPs to time multiplex output temps for two zones (UFH and rads).

Yes they can, mine has volt free contacts that allow two settable  flow temperatures for heating and two for cooling. You can only do one temperature at a time. So could us a diverter valve with microswitch to control it and simple time switch.

 

16 minutes ago, Beelbeebub said:

also wonder if you could do defrost cycles by switching to DHW coil

Not sure about that, mine inhibits defrost when doing DHW. You just compensate with slightly higher flow rate to compensate. So mean flow temp is ok.

Edited December 8, 2023 by JohnMo
Clarification of heating and cooling temperatures

[joth]

33 minutes ago, JohnMo said:

43 minutes ago, Beelbeebub said:

I'e be really interested if it was possible for HPs to time multiplex output temps for two zones (UFH and rads).

Yes they can, mine has volt free contacts that allow two settable  flow temperatures for heating and two for cooling. You can only do one temperature at a time. So could us a diverter valve with microswitch to control it and simple time switch.

 

The ecodan is slightly smarter in that if you only have one zone on it will operate at that flow temperature, but if both are on it will pump heat to the hotter one (or colder one in cooling mode) and use the electronic blending valve to maintain the milder temperature on the other zone

 

However, it is also dumber as it only has the two dry contact inputs (Z1 and Z2 resp.) and switching them between heating and cooling mode is manual setting change, or if you're feeling lucky via a seasonal schedule in the cloud portal.

 

[Beelbeebub]

3 hours ago, JohnMo said:

That misses the point I never really realised, if said zone is behind a mixer it doesn't count.

 

Which is why mixers should only be installed as a last resort. The only reason to have a mixer is having two zones that need to run simultaneously and one is significantly higher temp than the other.  The classic example being UFH downstairs and Rads upstairs.  Hence my musings about multiplexing....

 

3 hours ago, JohnMo said:

Yes they can, mine has volt free contacts that allow two settable  flow temperatures for heating and two for cooling. You can only do one temperature at a time. So could us a diverter valve with microswitch to control it and simple time switch.

does it allow for "seamless" switching between the flow temps?  I seem to remember someone saying their HP would stop and then restart at the changeover.  If it simply ramped up or down then it might work.

 

You could mod your current setup by fitting a 2 port valve on both the rad and ufh loops (or a 3 port depending on your pipework).  Then setting your blending valve to be the maximum safe temp.  In UFH mode, the low temp is output, the valve to the UFH is opened and the pump is turned on (this bit is optional, might not be needed).  The blending valve will go 100% hot trying to achieve it's set temp which is lower than the flow temp so you will effectively have an open loop.  When you switch to Rads, the UFH loop is closed off and the rads opened.

 

Just kicking ideas around! not actual advice!

[phykell]

On 04/12/2023 at 10:49, Slippin Jimmy said:

I've recently got quotes for heat pumps, and found one at £4,000 for a Mitsubishi 5/6kw Heat pump, and a 200L cylinder in the loft with 7 radiator upgrades after the gov grant. I'll be adding this onto my remortgage so it's costing a couple of quid a month for the upfront cost.

I live in a 2019, 3 bedroomed, small new build so it's very efficient, usually only need the gas combi boiler heating on for 2 hours a day max when it's currently about -1 degrees c. If i get onto the heat pump, I can cap the gas off and stop paying the standing charges for it.

My question is, I know heat pumps should be left on 24/7 at a set temperature. However, I could run the heat pump 4x cheaper than the normal electricity rate if I keep within those set times to reduce to 7.5p kw/h. If I set the schedule on the heat pump heating to only run between the above hours, as well as the hot water heating within those times, will it be enough to heat the house? We're comfortable with about 18 degrees, so don't need the house super hot.

I can only speak from experience as a homeowner, but take a look at the latest Vaillant Arotherm Plus as well. As I understand it, unlike some other manufacturers, Vaillant engineers are able to provide support over the phone and will visit your installation - I've had a good experience so far. My system fits in a relatively small plant room and has an excellent app which lets me track and store data on everything. 

 

Some real-world figures for you, using yesterday as an example:

Electricity use...

Heating: 24.3kWh, COP figure of 4.7

Hot Water: 5kW, COP figure of 2.6 (one shower in the morning)

Average COP figure of 4.3.

 

Running a heat pump 24/7 might not be necessary - it really does depend on your use of it. For example, there's usually someone at home at my house all day/night so it's important for us to maintain a reasonable temperature throughout the day. We have a "setback" temperature of 18 degC from 22:00 to 08:00 and 21 degC throughout the day/evening. The heat pump uses (outside measured) temperature compensation so it adjusts its flow temperature accordingly. The "aim of the game" is to only generate enough heat to replace what's lost - you probably know this from having an efficient home - I like to think of it as getting a large flywheel turning and only then needed to apply minimal effort to keep it running at a given speed. If your home is cold (e.g. you've been on holiday and had the heating off) then there's a certain amount of "inertia" to overcome so the heat pump has to use a relatively high flow temperature (my maximum is set to 47 degC) but it runs inefficently at this temperature, hence the difference in COP between heating and DHW (it heats the latter up to 52 degC).

 

In your case, you can run the heat pump at specific hours but you might find that your heat pump is having to work harder, i.e. the flow temperature has to be higher to get the house up to temperature. The issue there is that the higher the flow temperature, the less efficient the heat pump runs. For example, my home is a very comfortable 21 degC and whilst the heat pump is running, the flow temperature is only 36.5 degC so the inverter technology (it's able to modulate its running speed) means that it's running very efficiently (hence the good COP figure).