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Thread: Hometronic and Heat Pumps

  1. #1
    Automated Home Jr Member
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    Default Hometronic and Heat Pumps

    Hi!

    Does anyone know whether Hometronic is compatible with a heat pump, either ground or air souce?? Currently running on oil and the hometronic saves us lots of money as well as comfort value, but one company we've spoken too about changing to a heat pump says that it can't be used as the heat pump runs 24 hours a day to keep the house at a constant 20-21 degrees... Seems a bit mad.. Certainly if you want to save money.

    Also anyone any experience with heat pumps in general, and using on radiators (albeit oversized as they were as per 1975 pre-insulation and double glazing!)

    Thanks for any thoughts or advice!

    Nick

  2. #2
    Automated Home Sr Member NeilUK's Avatar
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    You can control most heat pumps fairly easily, I have a GSHP at home controlled by Hometronic. It sounds like you have come across one of the companies that uses professional salesmen who have little or no technical knowledge about hoe heat pumps work nor how much energy they can waste if not utilised/controlled properly. They are also often ignorent of the controls that are actually built in to the units they sell which specifically aim to prevent 24/7 operation at full output. Then again I have heard salesmen suggest that heat pumps are so efficient that if you are too hot then you open your windows rather than adjust the heat pump, what twaddle!!

    Now there are some issues that have to be looked at, will the heat pump have a separate buffer tank or is it an all-in-one. In it is all-in-one (as mine is) then you may have to leave a number of radiators uncontrolled to ensure a minimum flow through the heat pump. Also some heat pumps have no facility to allow external control. My unit is from Nibe and does allow an external controller to provide a heat demand signal. Most heat pumps also include weather compensation to vary the temperature of the water feeding the heating based on the outside air temperature - hotter water on cold days, cooler water on milder days.

    However you also have an efficiency issue when the heat pump is used with radiators unless they are significantly over sized. Normal radiator systems require the flow temperature to be as high as 80 degrees in winter to meet the heat loss from the house and the heat pump simply cannot provide this high temperature water from the compressor alone. Most units use an immersion heater to boost the flow temperature to this level which can be expensive if your house is large and/or you need this high temperature output for long periods. When you also consider that the heat pump is at its most efficient producing low temperature water this means that for most of the heating season you will be getting quite low levels of efficiency when used with a traditional radiator- at a flow temperature of 65 degrees a GSHP may have a COP (co-efficient of performance, e.g. how many units of heat energy you get out of the heat pump for every unit of energy used to run the compressor) level of less than 2, whereas with a flow temperature of 35 degrees (suitable for modern underfloor heating installations) the COP may be 5 or above. With the cost of electricity being so much higher than gas, oil & LPG then you may find that you may not even reduce your heating bills at all with a GSHP connected to radiators.

    Finally you also need to look at the electricity tariffs that are offered in your area to see if you have access to Economy 10 tariffs. These give you 10 hours a day of off-peak electricity usually split into 3 periods and can also make a difference to the running costs providing you can synchronise the off-peak periods with your need for heating.

    If you have an old inefficient boiler just now then you may be better upgrading to a modern fully condensing/modulating boiler rather than a heat pump. This coupled with Hometronic control will maximise the efficiency of your system especially if you cannot easily improve the insulation levels of the house or the air tightness.

  3. #3
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    Currently we're on an oil rayburn (480K - so it's a modern one).. Only reason for change is that the rayburn as a cooker just doesn't suit our lifestyle, so we use an electric hob and combi microwave, and the rayburn is just taking up valuable space in the kitchen, which we want to replace...

    Our oil tank is probably getting on for 35 years old and showing its age, so would need replacing. Also water pressure (or to be more accurate, flow) is very poor so a combi would be out of the question - BUT we've just found out the we have lead levels of over double the legal limit so need to replace the main anyway - 350m of private main! So a combi maybe back in when the pipe is renewed...

    Anyway - to cut a long story short, had quotes approaching 10k to replace with an oil boiler, booster pump and new high pressure hot water cylinder. And same company quoted around the same for 3 air source heat pumps and same booster set and tank. Is such a huge amout of money...

    The heat pump idea is more about it feeling very wrong to install another oil boiler - apart from the hassle of having deliveries and the smell... on the eco side...

    As far as the house goes - is an 1835 cottage extended in 1975 to roughly double size bungalow of around 160m2 area. Radiators are from 1975 spec. Since then, we've had all walls insulated (yes - believe it or not the 1835 part of the house has caivity walls!) and so has the loft. We never have the rayburn above around half boiler temperate - although I have never measured what temperature that actually is.

    I suppose the other issue we have is trying to place whatever we replace. Our whole objective is to clear the kitchen of both the rayburn and hot water cylinder to improve the kitchen... Ideally as much as possible would go in the loft. We've even had quotes for mains gas - but looking at 20k+.

    Hope this provides an insight - but would way that since hometronic install, have seen much lower oil usage.

    cheers

    Nick

  4. #4
    Automated Home Sr Member NeilUK's Avatar
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    A modern Rayburn is generally as efficient as any other conventional boiler as it is really a range cooker with integrated boiler. However a new condensing boiler will be far more efficient (does not have to be a combi as well, could be used with a conventional or pressurised hot water cylinder), especially if the radiators are over sized allowing lower flow temperatures to be used.

    Well if the heat pump you are considering is an air-source unit then I would be asking the supplier for a detailed breakdown of the COP for different outside air and water flow temperatures. Air source units are a lot easier to install, no need to bury several hundred meters of pipework in the garden, but they are also less efficient than ground source in winter when the outside air temperature is low. If you go to Wikipedia there is a useful chart that shows the typical COP values for different types of heat pumps at different flow temperatures.

    If you can estimate your annual heating load from your oil usage you could use this to guestimate the heat pump utilisation and running costs for a comparison.

  5. #5
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    maybe should just go with original plan and LPG! Although everyone seems to be going wild about it being so expensive... The GSHP was quoted by a very well known company without mentioning them, they're the ones that said hometronic definitely can't be used.

    A local guy has quoted for air source or oil, and he was more than happy that it was used, and actually encouraged it.

    We are in a very cold spot, very high up about 20 miles N of birmingham, we still see snow on the ground a week after everyone elses has gone. Also power cuts are common and we use a generator a lot, so again a down site of heat pumps or other electric heating.

  6. #6
    Moderator toscal's Avatar
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    If this is any help to you.

    I remember a friend of mine used to live in a 500 year old cottage. And they had a heat pump. I'm going back 20 years so it was probably one of the first. They had skirting board style rads with fins very early 70's in look. I have found a site with what looks like the modern equivalent http://www.technologymarketingmanage...asp?PageID=200

    They also had double glazed wooden frame windows and the house was never cold.
    hope this helps.

    Most heating systems stop when there is a power cut, as the circulation pump stops working unless its a gravity fed system I suppose. Also if you have a 3 way valve to switch from heating and hot water then a certain law states that it will be stuck in the position you don't want at the time the power goes off.
    Last edited by toscal; 13th June 2008 at 03:29 PM.
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  7. #7
    Automated Home Sr Member NeilUK's Avatar
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    It really does depend on who you talk to within a company, I have dealt with many heat pump salesmen and a few technical directors who swear blind that controls are either not needed or cannot be used with their products. So far I have found very few that actually do not allow external controls in one form or another to be used. There may be a need for some tweaking of the plumbing but it is normally ok. The difficulty is when the companies who distribute the heat pumps in the UK start to suggest that their warranty is void if you use external controls even if the manufacturer has provided details of how to wire them in and what needs to be done to make the controls work well.

    You are right to consider the implications of power cuts, even a small generator can usually cope with the small electrical loads from a conventional boiler fed central heating system. A heat pump is a different proposition - my unit has a 2.2kW compressor with soft-start control yet it still draws in excess of 30A when it starts up.

    LPG is certainly worth considering although prices could still be volatile with the ongoing speculation in the oil market. It might also be worth looking at wood pellet boilers if you have the space. Both will work well with your radiator heating and a high efficiency LPG boiler with fully modulating burner (such as from Worcester Bosch or Broag Remha) would likely offer the lowest annual running costs unless LPG prices go crazy and will also cost much less to supply/install compared to heat pumps.

  8. #8
    Moderator toscal's Avatar
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    I agree with NeilUK about some companies saying you can't do something this way or that way even though it either states it in the manual or on the manufacturers website. I've had a heating engineer fit a new thermostat to an existing system, and then say oh the boiler doesn't work you need a new one. When I told him he had fitted the wrong type of thermostat he said "no I'm a heating engineer and I know what I am doing". So I fitted the old one back and and guess what the boiler worked. We have a modulating boiler type from Bosch. I then told him he didn't know what he was talking about and that I have it working with the old stat. He then rather reluctantly admitted that he had never worked on this type of boiler before.


    IF power cuts are a big problem why not rather than use a generator go for some kind of solar powered 220 volt generator. If you go for a boiler then the circulating pump will probably draw less than an amp. My pump is rated at 80 watts or 0.364 amps. At this sort of current draw a self contained solar generator just running the pump would be possible. Statpower do some very nice 12v to 220volt systems. Ideally you would have a 220 mains input going into a converter and combined charger, and connect up a solar panel or 2 to this unit as well, or to a charge controller. So when you have power, you basically get your supply from the mains, and the battereis charge from the mains. And when you have a power cut the unit supplies your 220V via the batteries. All this takes less than a second its measured in milliseconds. Can't remember the exact time. And the solar panel will top up the batteries when the mains can't.
    Victron energy do a free book on solar power generating and conversion to 220 mains. The book in some areas is geared towards yachts and motorboats, but it still provides very useful information.

    for Statpower look here http://www.xantrex.com
    http://www.xantrex.com/web/id/25/learn.asp

    For Victron
    http://www.victronenergy.com/
    link for free book or to download a copy
    http://www.victronenergy.com/orderbook/

    Or replace the mains pump with a 12 or 24 volt one, and then there is no need to convert 12/24 volts to mains.
    Last edited by toscal; 15th June 2008 at 05:43 PM.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.
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  9. #9
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    Great info guys and food for thought. I think its always harder when you're replacing - nearly for the sake of it. There is nothing wrong with the 480K Rayburn we have, apart from the huge amount of space it takes and the fact we simply don't use it as a cooker. The beans on toast taking 45 minutes just doesn't work with a young family!

    Our current diesel generator is a 3.5kw one, and happily runs the house if we're carefull with using hungry appliances. The overhead cables to the village come in through cannock chase forest, so come down quite often. Since we've lived in the house 2.5 years ago, I think the generator must have been run for getting on 2 weeks in total. It is always nice to think we're one of the very few people in the village sitting nice and warm, drinking tea and watching telly, for all the racket it makes!

    Biomass boilers sound like a good option, but I think they do take up a lot of room and also cost the earth from what I've seen, so maybe all in LPG is a better option? Low runnign costs on maintanane and low outlay, probably means 10 years before you'd notice the difference to oil anyway?

    cheers

    Nick

  10. #10
    Automated Home Sr Member NeilUK's Avatar
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    Regarding LPG and with current prices I think you are right. Even wood pellet prices have doubled recently so it makes the comparisons of total cost of ownership of any period very difficult to predict right now. At least with LPG you know the boiler is likely to be easier to have maintained although you will have ongoing servicing/maintenance of the tank as well as the boiler with the gas being pressurised.

    If the 24kW output form the boiler easily meets your needs then I think you would be surprised by the efficiency improvements offered by a fully condensing/modulating boiler such as a Worcester Bosch Greenstar 30CDi. Because it can modulate the burner between 7 & 30kW based on the load from the system then it is a great match for fully zoned controls such as Hometronic.

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