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Thread: Programmable TRVs with new High Temp Air Source Heat Pumo

  1. #1
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    Default Programmable TRVs with new High Temp Air Source Heat Pumo

    Hi guys, I'm new to posting, but have been lurking for a while! I am after some advise please from whoever can give it, as follows. We are getting a 16kw Daikin high temperature air source heat pump installed at the end of March to replace the lpg boiler in our house and we are looking for the most efficient way of running it once installed. The main issue is that we are carrying out the install for green reasons rather than financial savings and we don't actually spend a great deal on heating and hot water at the moment (c 1050 per year). This also means that after spending a fortune on the new kit, I don't intend on spending "Honeywell" money to finish it off!

    Some background to our house:
    - it's a 5 bed detached house, built in 2009 (although to 2004 standards when the building warrant was applied for, so maybe some differences with insulation, etc)
    - we will be undertaking an attic conversion adding 2 further bedrooms (total of 7), plus 2 shower rooms (total of 4 shower rooms, 1 bathroom and 1 cloakroom)
    - in addition we have 3 public rooms, a kitchen, utility and very large hallway
    - total sq footage is increasing from 2300 to 2900ish
    - we have trvs in all rooms, excluding one of the 3 radiators in our hallway
    - we will be getting a couple of Dimplex smart rads. One will go in the hallway (not technically needed) and the other in the kitchen (needed to upgrade the output after I removed the second radiator last week when I remodeled the room)
    - hot water will be from a 260l unvented mains pressure cylinder (replacing a similar Megaflo cylinder) with thermostatic mixer

    How we currently use our central heating system:
    - water is heated 24/7
    - heating runs from 6:30am to 7:30am and from 4pm to 10pm weekdays; 7:30am to 10am and 3pm to 10pm at the weekend
    - Heating is turned off completely for 5/6 months of the year and we run the electric immersion heater for hot water. This works out effectively free as we have solar panes which offset the increased cost.

    Requirements:
    - I work from home a few days per week and my wife is a student nurse, so we are often home during the day in either the study, bedroom or kitchen
    - I am very prudent with money (or tight if you ask my wife!), so refuse to heat the whole house during the day while all of our kids are at school, hence my thoughts for why individually controllable stats would be good
    - any new trvs must be quiet. We have 4 kids and I have a scary wife that's already not impressed with what she is calling my new toy. If there is any excessive noise from electronic trvs then she will crucify me! She is a very light sleeper and she could be asleep day or night depending on her shift
    - did I mention it must represent good value for money and actually have a payback period, unlike the ASHP??!!
    - we have 4 chrome towel rails in the house with straight chrome trv valves and the thought of seeing the electronic / wireless valves on any of these would see my guts for garters from she who must be obeyed!
    - Excluding a pass through rad in the lower hallway, we have Myson 2 way trvs on all rads

    I've seen the Honewell kit and it would be simply way out of what I am willing to pay. I've seen the Conrad kit and it looks good, but I'm confused about what I will need (my wife said these are ugly though). I've seen etrvs and think the lack of a display on either the trv or remote is silly, but am aware of the iphone adapter which is available and we can use on my wife's phone. There's also the eQ-2 MAX! kit which looks like the maximum I want to spend, but I think would be noisy based on previous reviewers. All in all, I'm going round in circles now.

    So, this is where you guys come in please. What would you recommend, and if why?

  2. #2
    Automated Home Legend chris_j_hunter's Avatar
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    some thoughts :

    surely your new kit comes with controls ... ?

    not sure what's meant by a High Temperature ASHP - presumably it means it's designed to work with radiators ...

    basic thermodynamics points clearly to keeping temperatures down & changes slow ...

    the most important thing is to keep the temperature difference between heat-pump unit input (local ambient air) & heat pump output (water supplied by heat pump unit, going to the heat store) as small as possible - minimising this difference will have a big effect on efficiency & running costs ...

    radiators are not helpful in this regard - because they are generally so small, they need to be run relatively hot, 'though smart ones (with fan) should be a lot better ...

    next most important is to run it 24/7, to keep things even & gentle with small temperature changes - this will be more than helpful ...

    properly set up, your ASHP should be cheaper to run than a boiler using mains gas, let-alone LPG ...
    Last edited by chris_j_hunter; 9th February 2013 at 06:03 PM.

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    Hi, thank you for the reply.

    The new system comes with a wireless thermostat for the hall plus a programmer for switching the heating on and off. The difference between the heat pump we are having installed and the "usual" ones is that my one is designed to run at the same kind of temperature as our old LPG boiler. It will self modulate at between 60 and 80 degrees celcius depending on the internal and external temperatures, with 75 degrees set for when external temps are around -4. It will take between 20 and 30 minutes for the flow temperature to reach the operating temperature, so a little longer than the 20-25 minutes currently; but all in all it will be roughly in line with the flexibility and "instant on" we currently experience.

    I have received detailed information on how much the heating will cost to run based on the average number of hours it's on, as follows:

    Number of Hours Approx LPG Cost () Approx Heat Pump Cost ()
    5 1619 1117
    12 2127 1426
    14 2230 1488
    16 2314 1539
    24 2464 1603

    We do tend to keep the house fairly cool at the moment, but I am willing to pay more to have a more efficient system in place. You will see above that we are only using around 1,050 per year in LPG at the moment, so I am expecting an increase, but due to the quick response of the new kit I was looking to effectively shut down 75% of the house through the day to minimise the difference in cost.

  4. #4
    Automated Home Legend chris_j_hunter's Avatar
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    sounds to me like the controls it comes with would be enough ... it will have sensors in the outside heat pump unit, too, so all will be covered ...

    so long as you set it up optimally & use it optimally, it should cost you less to run than your current set-up - perhaps in proportion to the figures quoted ...

    with an ASHP - and possibly your current set-up, too - heating your whole house 24/7, with set-backs, would likely cost you less than switching on & off for substantial parts of the day - rapid catch-ups are very inefficient, and cold spots can be causes of condensation problems, on walls & on things ...

    certainly, though, various strategies should be tried, to get the measure & be sure ...

    NB: difficult to believe a system that cost more to buy & more to run would be more green !
    Last edited by chris_j_hunter; 9th February 2013 at 06:13 PM.

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    Thanks again Chris, but what do you mean by set-backs? If I could leave the heating on all day but reduce the unused rooms to switch off at say 14/15 degrees when they're not being used (between 8 and 16 hours per day depending on the room) then surely that would save money compared to having the whole house set to whatever the TRVs are set at without touching them? I am simply too lazy/forgetful to go around and adjust them morning noon and night so I assumed the electronically adjustable TRVs would make cost savings??

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    Automated Home Legend chris_j_hunter's Avatar
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    set-backs is just the business of setting a slightly lower temperature for part of the day - overnight, usually, but can be any time ... and it would be surprising if your ASHP didn't come with the facility to set them ...

    the saving from 24/7 comes from several factors - 1) people expect fast response, so whang it up if it feels cold, which forces the heating source to deliver higher temperatures for a while (inefficient because the delta temperature from input ambient air to boiler / heat-pump output goes up, which increases losses & causes thermodynamic inefficiency) - 2) if the heating system is brought-on only just before it's needed, same applies - 3) if the house is cold, the heating radiators need to be a fair bit hotter to compensate, which is inefficient again, for the same reasons - comfort being largely determined by the radiant environment of the house, and we get uncomfortable if the house takes too much heat from us, as will happen when some or all surfaces are too cold) ... etc.

    so 24/7 with small set-backs should be best - the more-so with ASHP, because their heat-capacity is generally a lot less than that of a regular boiler - not a bad thing, just needs to be taken into account ... eg: your 16kW ASHP might take up to around 4kW in mains electric, as against a gas boiler's 24 or 36kW or more, so things need to be managed more delicately !
    Last edited by chris_j_hunter; 9th February 2013 at 08:06 PM.

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    had a quick look for manuals for your HT ASHP ... of the various options, best guess is that it's one of their Altherma range, albeit I couldn't see a 16kW one ... if so, then it looks like set-points & set-backs are to be set via their thermostat, which looks to be pretty comprehensive :

    http://www.daikinac.com/residential/...c=docs&page=29

    http://www.daikinac.com/DOC/Product%...-%20Daikin.pdf

    also had a look for eTRVs, and found a few, including :

    http://www.sangamo.co.uk/shop/Choice...1-details.aspx

    which look like a good idea, 'though the pay-back might be rather long ...
    Last edited by chris_j_hunter; 10th February 2013 at 12:03 AM.

  8. #8
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    Hi,

    Yes, it's an Altherma 16kw high temp unit, as mentioned here: http://www.vent-axia.com/product/dai...door-unit.html

    I thought of maybe running these: http://www.gasproducts.co.uk/acatalo..._.html#a635001
    but the issue is that there are many reviews saying that they are noisy when the actuator releases or closes the TRV pin below (electric motor).

    Is there anything similar out there which is quieter like the etrv without the cost of the etrv? I think they are a great idea to create zones in the house, maybe reducing bedrooms and unused rooms to 14/15 degrees, bringing them up to temperature half an hour before the rooms are due to be used, thus saving energy and meaning that the heat pump can be run all day without me getting too weary of the cost of heating an entire house.

  9. #9
    Automated Home Legend chris_j_hunter's Avatar
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    see they quote a CoP (heat out / power in) of 2.88 - for 7degC ambient & 65degC HP unit output (what they call leaving water temp') ... this seems extraordinarily good - for a deltaT of 65 - 7 = 58degC, most ASHPs would give a rather lower CoP, of around 1.75 ...

    not sure how the Altherma works, or why it should be so much better than the competition - the blurb mentions cascading, which would seem to imply a two-stage process, which might be expected to be less efficient, not more ... (?)

    there's a Swiss website, that gives data from tests of a large number of ASHPs, and (when we looked) all of them seemed to come-out close to normal ... there's a summary here :

    http://www.academia.edu/1073992/A_re...of_performance

    an Altherma is mentioned (under other manufacturers), and the figures given are normal, not extraordinary !

    CoP will vary with the deltaT - increase the 65degC and/or reduce the ambient, and it will go down ... eg: 7degC ambient & 80degC would normally take it down to about 1.25, and 0degC ambient & 80degC down to about 1.00 - conversely, going to 20degC ambient & 50degC would up it to almost 4.00 ... so going for 80degC will cost you dear, it's worth running your heat store as cool as possible !

    IIRC, controllable TRVs are usually wax driven, using a heating element, rather than a motor - eg: those by Sauter - presumably for quietness ... eg:

    http://www.idratek.com/public/docs/d.../RVA001_DS.pdf
    Last edited by chris_j_hunter; 10th February 2013 at 11:57 PM.

  10. #10
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    Good COP bad COP. It's a good idea to make a matrix of COP vs air temp vs. delta T raised so you can see whare to steer your project. What you are likely to see is that daytime running is better than night time (so you'll need a big tank to store the energy). You can further raise the COP by pre-heating the outside air as much as possible - eg polytunnel, ground pipes, green house, house air exchange, sunny position. Then you can raise the COP by lowering delivery temps and that implies swapping some of the rads to fan-coils, certainly in bedrooms where a quick blast in the morning is often enough. High temp ASHPs have a 2 stage compressor which obviously has to do more work to get to 60C etc. You'll also see that the power delivery of the ASHP falls dramatically with cold air so do your sums around 10kW rather than 16kW
    I recently did a newsletter item showing that an all out attack on COPs assisted by big solar panels and a big pair of tanks can get close to the price of wood energy and, pf course make gas look totally silly.
    Finally - don't assume that connecting an ASHP to a heat bank is just like for gas boilers... it's a bit more involved because you have to stop the higher flow rates from destroying the stratified tank and thus making recovery times very long. You need to be extracting heat via a plate heat exchanger for DHW as that not only gives huge power on the lowest supply temps but also allows use of the hot water at the top of the tank.

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