@william1066 Thanks for your detailed response.  That's amazing to have been able to maintain 20c+ with 3c outside temp using only 27.2c flow.  Do you also have a flow regulator installed to measure the flow rate in the system too?

For the last month I have taken daily meter readings, for my 17kw grant ASHP the least usage being 25th Dec with 37kw/h, the worst being yesterday at 93kw/h .... pre ASHP days we would use 15 to 20kw/h per day.  Theormostats currently set to 19 degrees for 24 hours with 45degrees at -2 for the weather comp and 55 for the DHW which I just moved to afternoon.

I have tried many tweaks, but by far the biggest variable that I see is one I cannot control and is the weather. Last few days where temp average is below zero has seen constant cycling with defrost cycles ..... I cant believe the system design that steals heat from your house making the ASHP work harder and cycle more .....

My spreadsheet told me switch off economy 7 meter which was simple with a quick phone call to Eon.

I could also see the heat demand coming on at different times in the 4 different heat zones which seems inefficient to me. So now I have merged all the UFH zones into one and the rads into a second zone ..... I may even move the wireless rads thermostat into extension so they both run at same time to see if that helps .....

I think the next best thing I can do is fit a wood burner in our extension and use that to reduce the load on the ASHP especially sub zero days.

This whole ASHP experience has been a yoyo between good and very bad ..... 

Posted by: @soniks

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That's amazing to have been able to maintain 20c+ with 3c outside temp using only 27.2c flow.

There is quite a lot of thermal inertia in the concrete, so I really need to get the outside temperature and concrete temperature into the data set and look over a couple of days to see what is going on in case lag is hiding something.  Every degree the concrete drops in temperature releases 2.8 kW of heat into this room, that drop may not be noticeable.  Having said that ....

This room has an average heat loss (old and new bit) @-2 degC outside of 67 W/sqm (2000W in total) so well within the limits of a new and well insulated solid concrete floor with UFH.  Though to be honest, I was not 100% sure how it would turn out, despite looking into the maths of this all.

I also did two things, 100mm pipe spacing and max 50m loops with the UFH pipes.  With the aim of being at the most efficient end of flow temp, delta T and to enable high flow rate. (at the expense of a lot more UFH pipe and larger/more expensive manifolds). 

In terms of UFH, I have 5 circuits at 2 l/min each so 0.166 l/s in total.  Put this into  kW = l/s ⋅ 4.18 ⋅ ΔT.  [0.166666667×4.18×3] ... out pops 2kW of heat.  So as long as I can get the floor surface temp to enable 67 W/sqm (using formulae below) I should be ok for 99% of the time.  [i.e. -2 degC or above outside]

Above table is using floor emitter rate formulae that I got from somewhere for concrete - don't recall where.  You don't really want to go over 27 floor surface temp afaik, not sure why.

Concrete Floor Emitter Output = 8.92*(Fst - Rt)^1.1 = watts per sqm  (fst is floor surface temp and rt is room temp).   I don't yet have accurate data for the in out flow temp into this rooms UFH or the floor temperatures, but will look to getting that data at some point.

I have an approximation of flow rate from the Grundfos pump modbus interface (+-10%), hopefully I will get the modbus interface in the heat pump tomorrow and connect that up as well then the floor probes and some other bits and pieces. 

** disclaimer ** - please verify these formulae with a reliable source before using them for anything at all - they are provided without any warranty - thanks.

Posted by: @denevil

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My spreadsheet told me switch off economy 7 meter which was simple with a quick phone call to Eon.

Interesting, I may need to do the same.  I am almost at the 1 month point since switching on my ASHP.

This whole ASHP experience has been a yoyo between good and very bad .....

There has been some mention on this site about better designs for the external coils that don't need defrosting as much, so for those up north, I can understand some level of frustration.

On the other hand, my view is that an extra jumper for one or two weeks a year is a small price to pay to move to renewables.  In parts of Africa they tolerate a rather chilly 4-6 weeks in their houses every year, because the cost of building a house to high comfort levels for 99% of the year is just not worth it.

MCS goals are 99%, I am working to a much more modest 90-95% of the time.

My only complaint with my install so far, is the hot water.  But I chose to stick with my vented thermal store with its back boiler and solar thermal and save money on a new cylinder, against advice from a number of people.  I think I will be able to work through those, and have modified my tank a bit, one more weekends worth work and I think I will be sorted on the hot water.

Does anyone know the purpose of a volumiser tank in a heat pump system design.  I have one installed based on the schematic attached below but have no idea what purpose it servers or whether it leads to an efficient design

Dow

Posted by: @soniks

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Does anyone know the purpose of a volumiser tank in a heat pump system design.  I have one installed based on the schematic attached below but have no idea what purpose it servers or whether it leads to an efficient design

 

 

Dow

My understanding is that the volumiser is added, as the name explains, to add water volume to the system. The purpose is to store heat energy for when the heat pump performs a defrost cycle.

To defrost the heat pump evaporator quickly, particularly when the outside air temperature is around or below zero, it is necessary to take heat energy from inside your home, in particular from the water within your central heating system. Larger heat pumps obviously require more heat energy to defrost, so will require a larger volume of water, which could be the reason a volumiser tank was installed in your system.

It has no detrimental effect and is certainly much better than installing a buffer tank, in fact it may help to reduce short cycling during warmer weather conditions.

Also, depending on the system design, can add the required volume of water for DHW cycle - mine was too close for comfort - I added in the 30L volumizer for this reason alone.

There is no need for it on the CH circuit.

@soniks for January so far between 43 and 100 kw per day with EV charging. It's hard to see what is from the hp though as grant has no direct way of comparing. I'm now experimenting with heating the heating water with hp and immersion overnight on cheaper tarrif. Then setting hot water on economy setting from grant controller for a couple of separate hours through the day. Although again not sure I can work out comparisons as have hive installed and another timer connected to cylinder although I've synced them all to same times, I'm not convinced the grant controller is doing what I've programmed.

@soniks Do you have a grant HP? If so how did you get that data?

FYI the Grant combined volumiser / low loss header in my system has an immersion. The immersion doesnt connect to EP001 and instead connects directly to the ASHP pin 46 (figure 4-5 in LLH manual).

By default this is DISABLED,  you can enable it and set it to one of several modes. It has a "supplementary heating mode" which can be used to help the defrost cycle as well as to provide extra heating help when it gets very cold. See Table 5-1 / 5-2 / 5-3

For defrost help I used

4600=3 (enable supplementary mode)

2620=2 (enable during defrost)

4623=30 (outgoing water set point during defrost)

5146=1 (backup heater)

 I left and didnt take suggested new values for

4613=5  (Outdoor temp to enable backup heater supplementary mode)

I think the following default params provide a smoothing function .. ie less cost, .... will experiment with them later, for now left more passive

4604=5 

4605=600

4614=5

I did set

4614=2 from 5

Need some time to see how much it helps though I think its promising in reducing the nighttime constant defrost cycling

@denevil let us know how you get on? I'm finding it hard to gauge at the moment with it being a little milder, but will be looking at reducing the flow further but the pipes have a long run so dont know if that makes any difference?

Heating the hot water actually uses less electricity than I thought it would. There's also a vortex blue one pump to boost the hot water circulation when required which does sap a bit of electricity when used.

@bretix when I had it installed I went with the metering and monitoring option which allows my to track the various metrics that are captured and then made available through the passive system installed.

I think you can add the metering and monitoring as a retrofit and there is an open source api that can be used.  I saw a video on it on the heat geek youtube channel.

Perhaps do something like that if you want to monitor the system.  I have to say I think it's so useful to understand what's going on with the heat pump and efficiency