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Discuss Martinplumber in the Renewable Energy area at

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  1. Martinplumber

    Martinplumber Guest

    Hi,I am doing a large new instalation of a ground source heat pump with underfloor heating to three floors having 7 large manifolds, plus hot water etc.My question is about the hot water side. As I have mentioned this is a large property and it is thought having a electric pumped hot water loop with two 300 litre hot water tanks next to the heat pump and buffer tank is the best method of delivery the hot water to the nine bathrooms, wc's kitchen, utility room etc., But I can't get my mind around thinking how having a permanent pumping of the hot water is not a very green idea and what of the balancing of the hot water pressure with that of the cold water to all the showers etc? I am open to this method but presently my preference is to have three water water tanks in their best positions which can supply all of the water within a suitable distance and keep the water pressure balanced throughout, although saying this there are two water mains to this property. This however I would have thought not present a problem as long as they can both be turned on/off together and with suitable notices and making this aware to the owners and having check valves installed on each main by the stop cocks? The considerable pipe-work loop to the the underfloor heating manifolds which starts with some length of pipe having a 50mm bore then reducing en-route down to 22mm at the furthest distance manifold valves. this loop could be altered to allow heating of the hot water tanks coils with suitable valve controls albeit having higher heat pump water temperature, and thereby also saving much extra pipe work?The other thing is there is a two phase electric supply to the property. One having a 3.84kw of PV panels on one phase and the other having a cheaper off peak supply to mainly the heat pump and hot water tank immersion heater top up for use in the early hours of the morning.I should be glad of any input or thoughts from any interested person?Many thanksMartin
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    whats your background ? eg big installations (schools hotels etc) if not get a m and e contractor/consultant
  3. SimonG

    SimonG Trusted Plumber Top Contributor!!

    Didn't get past the first few lines, but yes, what Shaun said :)
    • Like Like x 2
  4. Nostrum

    Nostrum Plumber GSR

    Hi Martin,

    First thing is to see how you can control the temperature of multiple cylinders via the heat pump controller. That may be an issue depending on what kit you're using.

    Sounds like an interesting job.
  5. Sparkgap

    Sparkgap Active Member

    Are these unvented HW tanks? Also, how does the CoP stack up for getting the higher temps for hot water? I know GSHPs have higher CoP than ASHP but presumably it would go down as the outlet temperature goes up.
    As for energy losses by having the cylinders nearer the points of use, depends on how far the circulation goes and how well the pipes are insulated. I've just designed a HW system for a factory which has about 40m run from water heaters to furthest point of use and total heat losses of about 1.5kW. If you've got central hot water with multiple cylinders you've got good recovery and backup. If you spread the cylinders around with each doing a few bathrooms you reduce the HW losses slightly (but lose more on the mains to the cylinders due to higher temps) but lose the redundancy.
    Did a 50 room mansion 5 years ago where i was going to put three cylinders around the place, but after the architect and client faffed around with the room layouts there was no space for them and ended up in a central utility cupboard with pumped circulation. Works alright.
  6. thompsonbrown

    thompsonbrown Plumber GSR

    My question is about the hot water side. As I have mentioned this is a large property and it is thought having a electric pumped hot water loop with two 300 litre hot water tanks next to the heat pump and buffer tank is the best method of delivery the hot water to the nine bathrooms, wc's kitchen, utility room etc., But I can't get my mind around thinking how having a permanent pumping of the hot water is not a very green idea and what of the balancing of the hot water pressure with that of the cold water to all the showers etc?
    When you say pumped do you mean circulated using a bronze pump. If so a well lagged hot water loop might be more cost effective than running off dead legs to get hot water to the furthest bathroom taps?
  7. Martinplumber

    Martinplumber Guest

    Hi Guys,

    Many thanks for all your advice and questions requiring further information. It is really good to have some dialog with other people who have some experience in such matters because they are really very thin on the ground. Even in my limited experience I have found even the manufacturers and major suppliers of heat pumps and renewables don't always get it right. The first half of this instalation covering half this new property we were told we would only need one circulating pump but soon found this didn't work. Plus where I trained to get my certificate for the installations they even under estimated the size and number of their own bore hole to deliver their own heating needs from a gshp when it iced up majorly in the first year. So I like to not just take their advice without questioning it, because at the end of the day they are mainly there to sell you their products and not always to interested after having made the sale.

    To answer some of your questions, Sparkgap and Nostrum, this is a new instalation with new unvented 300 litre hot water tanks. This is my property and so why I want to get it right. It has a distance from the heat pump to the manifolds of approx 50metre run of pipe (100metres including return) The Cop you are correct does reduce quite significantly from 4.2 for underfloor heating down to something like 2.4 for hot water heating. The pipework to have good insulation plus much of the pipe runs are also in an insulated void as well. My view is if it's has a pumped loop the hot water is in the pipes for 24 hours a day so as well as having to pay for the running cost of the pump/pumps there is also the greatest potential heat loss from this system with heat loss wastage getting past the insulation?

    You are right Nostrum the biggest hurdle is how to control all these valves to combine the hot water with the underfloor heating if the combined system is to be implemented, and I am open to any advice or input.

    Anyone have any views on the balancing of the water pressure with the pumped hot water system? That is another of my worries using the pumped hot water loop system.

    Thanks for your time


  8. oz-plumber

    oz-plumber Plumber

    Re: Pump pressures. You will find the circulating pump will not increase the pressure of the water in the system, it is there to keep a flow of hot water around the ring main.
    Generally when a tap is opened, a non-return valve will stop the flow of water through the pump.
    Without going into in depth technical reasons - just exclude that from your worries.

    Balancing shouldn't be too much of an issue either. I take it that the ring main will be a minimum temp of 65C. You will need tempering valves for each individual bathroom.
    With a correct set-up balancing of the water flow through these valves can be achieved relatively easily.

    Re: Heatloss through ring main. You will get some heatloss, but it will be minimal, if insulated correctly.
    If the pipe is sized correctly, the pump sized correctly, the heatloss will be equivocal to the heatloss from the cylinders.

    As for being green and energy efficient, you will only be able to do so much, particularly on a system of that size. But do what you can because it is a saving on money spent on energy.

    Out of interest, what is the place for - family home or something else?
  9. Sparkgap

    Sparkgap Active Member

    Hot water circulation and pressure: if you're running an unvented system a circulating pump will make virtually no difference to balanced pressures for showers. Usual unvented pressures are about 20-30m head equivalent while a typical HW circulating pump may generate 0.3-0.6m so any pressure difference is minute. Circulation means you don't have to wait ages running off all the cold water in the pipe before it gets hot and by keeping the hot water circulation temp high enough it helps prevent legionella. Another option used where they don't have circulation or a few long runs of pipe is to have trace heating tape to keep the pipe hot, but that means you are almost using electric to heat your water and still need decent pipe insulation. Either way, unless you've got the heat pump, cylinders and outlets all close together you're going to use electric to shove water around somewhere and this is the best way.
    You could go 'old skool' and look at gravity circulation :rofl: which doesn't need a pump but suspect you might lose even more in heat than you save in electric! Besides, modern pumps are pretty skimpy on power consumption. Do you actually need the HW circulating 24/7? Having it only running when people need it would save some money.

    When you refer to combining the system and controlling valves etc, I assume you mean making sure the system will cope under design conditions with both? I take it you've got a buffer tank on the GSHP which should provide a reserve for such occasions, just make sure it's sized correctly.
    As for sizing GSHP/boreholes etc, I believe the norm is to do a test beforehand to check what sort of flow rate/heat transfer can be taken from a borehole as this is dependent on geology/depth/ground conditions etc. I've mainly dealt with ASHP and the effects of outside temps tend to be more pronounced: I've mentioned elsewhere about a recent installation where the consultants/manufacturers came up with a certain size of unit, but when we queried that their design temps were 7C outside while ours were -3C for full heating output they had to amend the plant size up by about 30% due to the lower output at the lower temp. I have seen some jobs where they have a nice economical heat pump, then slap on several kW of electric heater for when it gets really cold and the heat pump can't cope!
    Last edited: Nov 17, 2015
  10. Worcester

    Worcester Plumber

    The biggest question is which heat pumps are you proposing as they differe quite fundamentally how they heat hot water and manage the heating of it.

    1) Whose GSHP's / What spec have you chosen?
    2) What's the Heat output at B0/W? What W are you designing for?
    3) What's the peak kW demand on the property?
    4) What the total kWh/annum from the heat pump?

    The answers above will have a MAJOR impact on how the returning secondary (colder) DHW affects the heat pumps.

    5) if you're considering running the heat pump(s) on offpeak electrcity, what size buffer tank are you designing?

    6) Are you MCS certified?

    7) How are you proposing to manage the timing of the heating for the DHW cylinders?

    It would be better to run the DHW on a completely separate (set of) circuits direct from the Heatpumps.

    Insulate ALL pipes except those specifically designed to emit heat - especially the primaries to and from each of the DHW cylinders.
  11. Worcester

    Worcester Plumber

    If you've got 50m from the heat pump to the manifolds - is the heat pump in a separate building?
    If so a highly insulated heat main may be the best way to get the flow and return to and from the heatpump.
    Wherever it is those runs should be well insulated. 25mm ideally 19mm absolute minimum.

    The DHW secondary circulation pipes also need to be insulated
  12. Unregistered

    Unregistered Guest

    Hi Sparkgap & Worcester,

    Many thanks again for for your comments and input, this all very helpful and much appreciated? To answer some of your questions, the heat source for the heat pump is from nearly a 1000metres of underground pipe work in our field and the heat pump is situated in our attached garaging adjoining the house and the existing pipe work is very well insulated with 25mm lagging, and I am MCS certified to install heat pumps, pressurised hot water cylinders etc.

    This system has all been designed to accommodate all the domestic output of those living here and with a pumped circulating hot water supply. But I cannot see even though I appreciate the pumps use little electric how pumping hot water around 24 hours a day is better than using well placed hot water tanks? Also thank you Sparkgap for your bit about the pumped water pressure that is good to know and will help me in my decision of which way to go.

    i know the pumped hot water is the way all the designers and suppliers have gone down for such wide spread domestic use but I wonder is it because it's the way they always do it, and nobody seems to questions it, and perhaps because it is less complicated to install? But I keep thinking of all that piping hot water being pumped around even in the best insulated pipe work how it must lose a considerable amount of heat. Consider if you would that probably throughout April - November the underfloor heating in any new built house is not required at all because of the high amount of insulation in all the floor, walls and ceiling etc., which now means you need hardly turn any heating and only a little heating even in the winter months, especially when it is as mild as it has been. Then all the pipe work to the U/f/h here shall be standing idle for all these months, when it could be also used in the heating of the hot water tanks by default on this pipe work to come on each night with the cheaper off peak supply to heat the water tanks? By the way there is a 150 litre buffer tank on the run by the heat pump. The emmersions could then come on for say an hour to top up the hot water to bring the tanks up to 65-70 degrees as required and then around 5am if the underfloor heating were calling for heat using a time switch and room controllers the underfloor heating then opens the valves to those manifolds calling for heat to then warm up the house?

    Is this a ridiculous cenario I am contemplating which might be too complicated and risky or is this a better more efficient way of utilising one considerable length of pipe work loop instead of two and a more efficient way of saving electricity with 24 hour pumping and the inevitable heat loss this must to some degree cause? That is what I am trying to decide.

    Many thanks again for all your help and input.

    Kind regards

  13. Worcester

    Worcester Plumber

    What is the heat loss for the property ? 1000m doesn't sound anywhere near enough based on your description so far.
    The heat pump is a brilliant solution for a well insulated property
    I'm really concerned that you don't know how to design this and you will end up with a system that just won't work
    so you

    You need to answer my previous questions before anyone give you any more help..
    • Like Like x 1
  14. Sparkgap

    Sparkgap Active Member

    Back of a fag packet calc: typical HWS pump about 20W, therefore running 24/7/365 uses about £27 of electric at 15p/kWh. If you add in 1" insulated pipe for 50m at about 10W/m losing heat from the GSHP at about 4.3p/kWh it loses about £190 worth of heat in that time. Obviously if you only have the HWS circulating for half the time then the costs halve as well.
    If you have your cylinders at the other end instead, and only a short run of circulating pipework you lose less from the HWS but more from the mains to the cylinders (in this case because of the higher primary temp the losses would go up 50% for the same size pipe) plus you'd need a more powerful primary pump=higher running costs, so you'd probably save very little if anything.

    From the sound of it then you're looking at using the heating mains around the house to feed the cylinders and manifolds and zoning using local motorised valves. Fine, just means the mains have to be sized for the increased load but perfectly acceptable. If you're also using the immersion heaters to top up the hot water (I take it the GSHP gets it up to about 50-55C and the immersion does the rest) then that would add to the running costs if you had long runs of circulating pipework.
    Pumped HWS is usual in commercial installations and larger domestic ones where you usually have all the plant in a central plantroom or aren't able to have cylinders near to the main points of use. Also, if you've got sinks or whatever scattered around the building you need circulation unless you are willing to accept lots of water wastage drawing off cold water from long dead legs.
    • Like Like x 1
  15. Worcester

    Worcester Plumber

    All that's good there are still fundamental issues with Martinplumber's designs though - for example Heatpumps work on a 3 port diverter valve, so where will he put the buffer tank, how / why would you share the flow/return with the 7 heating manifolds.

    This is a very straightforward system, being made complicated by the OP, who seems to lack fundamental understanding of heat pumps and plumbing systems and building regulations and MCS requirements and says this is for his own house, and the VERY worrying thing is that he is MCS certified ..

    7 LARGE Heating manifolds 3 x 300 litre DHW cylinders, unless this is a passiv haus, (or close to it ) then 1000m can't be any near adequate, unless he got hot rocks... Round here it works out in the order of 100m/kW so that's only 10kW ..
    Last edited: Nov 18, 2015
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