Part Thirty Three – System Details And The Bathrooms

This thirty third entry was published originally by JSHarris on the 4th September 2014 and received 2,097 views on the closed forum


Following a few questions on the old Ebuild forum, and as I’ve had a serious re-think after some experience of the way the house behaves through a winter and most of a hot summer, I thought an update on the final system I’ve installed might be helpful. The most important observation is that heating is not an issue, in fact I very much doubt if the house will need any significant heating in winter, as it gets very warm just from the heat of the occupants. Working in it over December and January we found that tee shirts and open windows were needed by mid-morning and we never once needed any heat. In fact we had to stop using the 400W halogen work lights and replace them with low energy ones, as one of the halogens running overheated the house pretty quickly even in cold weather.

The first observation is that cooling is far, far, more of an issue than heating, by a long way. I’ve deliberately limited the window sizes on the South elevation, and added an extended roof overhang to provide some shading to reduce solar gain, but the East facing windows in the second bedroom and the kitchen still provide a substantial amount of unwanted solar gain in summer. The house overheats unless it is actively cooled, even on days like today, when the outside air temperature only reached around 22 deg C. Without cooling the house would have been be up in the high 20’s today, just from some very limited solar gain.

There is are several lessons here for anyone planning a similar house. The first is look closely at the microclimate around where you want to build your house. Because we dug our house 2.5m down into a bank, two sides (the North and East) are very well sheltered. This is good in terms of reducing heat loss, but it does mean we have created a sun trap, with insufficient wind (because we are at the bottom of a valley) to provide any appreciable cooling. We can easily get air temperatures of well over 30 deg C on the north side of the house, just from the effect of the sun warming up the big retaining wall and heating up the air locally. This air is then drawn in to the MVHR intake and heats up the house, even with the MVHR on full bypass.

Luckily I spotted this effect when we were doing the ground works (where we saw temperatures of over 40 deg C in that dug out corner last July (2013). This meant I changed the MVHR I was going to buy for the much more expensive Genvex unit, which has an in-built air to air heat pump that can heat or cool the supply air to the rooms. This works reasonably well, but cannot cope with very hot weather, as the maximum cooling capability is only about 1kW, and the solar gain can easily be two or three times this in sunny weather.

By a stroke of pure good luck I discovered that the ASHP I’d bought (which is way too big, but was a surplus deal, so came at the right price!) is reversible. After much experimentation and head scratching I managed to reverse engineer the control system – the manufacturers are really just importers, and don’t have a clue as to how their kit actually operates or is controlled, so the documentation is dire. What I found is that the ASHP has a set of no-volt contacts that control it when it’s powered up. These have several functions, but the only two I’m using are those that turn the ASHP on and off (just a contact to a common connection) and one that switches between heating and cooling modes (closed to the common for heating, open for cooling). This made being able to reverse the ASHP to cool the floor a sensible thing to try in hot weather.

Much to my surprise, cooling the ground floor is remarkably effective, far more so than running the MVHR in cooling mode. I think that the primary benefit is that by cooling the floor to 19 deg C much of the solar gain is reduced, as a fair bit of that comes from the sun shining through the windows and heating the floor up, which then heats the air in the house by convection. By cooling the floor this heat is removed before it can heat the air in the house. Just running the UFH circulating pump will often do the job, just by transporting heat from the warmer areas of the slab to those that are relatively cool at the back of the house, which is OK for a day or two of hot weather, but for a prolonged hot spell the ASHP needs to remove the heat to stop the whole slab getting too hot (I’ve had the whole slab up over 23 deg C just from solar gain).

In order to make cooling the slab work I’ve had to redesign the heating/cooling system quite a bit, and do away with using the buffer tank in the UFH circuit. If I were starting over I’d not have the buffer tank at all, as it isn’t now really needed, but as it was installed, and as it was accidentally supplied with an indirect coil, I decided it was easier to just keep it in place and change the pipework around. So. on the ground floor this is the system I have (the pdf is easier to read that posting an image):

Heating and cooling system

And this is what some of it looks like, fitted under the work surface in the utility room, right next to the cupboard that houses the buffer tank:

The manifold is a standard unit with a low energy Grundfos pump, set to run at its lowest speed. It has a thermostatic mixer valve that has been adjusted to never allow the flow temperature to exceed 25 deg C, which is still higher than I would like, but does improve the slab response time if it needs heating fairly quickly. The pump and thermostat is turned on and off by the time switch, so the pump runs during the day, from early in the morning until 10pm. Even if the heating/cooling system isn’t actively doing anything the pump stays on, just to even the heat out around the slab. it’s a low power pump, and is mainly running when the PV system will be generating, so it only has a small impact on our overall energy consumption.

The small blue unit at the bottom is a 12V operated motorised ball valve. This was used for two reasons. Firstly, unlike normal central heating motorised valves, a ball valve is an absolute seal when closed, which is essential here as the buffer tank side can be warm (35 deg C or so) whilst the ASHP side can be quite cold (10 deg C or so in cooling mode). Even a very slight leakage across a spring loaded central heating type flapper valve would cause appreciable losses. This valve is switched by a home made thermostat/controller, that having moved the valve from one position to another turns off all power to it (although the valve only needs 60mA at 12 V to operate and only has a 15mA standby power consumption). This valve is opened whenever the ASHP is set to provide heat, and closed whenever it is set to cooling mode. In summer I suspect it will stay closed pretty much all the time, so the buffer tank won’t do anything useful at all, and the hot water will come entirely from the immersion heater driven by the PV array in the roof.

The controller is the uppermost white box, with the display. This sets the temperature of the slab and the switch provides a way of just turning the system control off, whilst maintaining the display. The controller has two sensors, one embedded in the floor near the North side of the slab, more or less in the centre (and well clear of any UFH pipes), the second is in a sheltered position poking out of the North wall of the house, to measure the outside air temperature. The knob sets the desired slab temperature (not the room temperature, as this is a slab stabilised control system) and incorporates weather compensation whenever the outside air temperature drops below 10 deg C. This works by increasing the set slab temperature by 0.1 deg C for every 1 deg C drop in outside temperature below 10 deg C. This should pretty much match the heat loss rate increase with decreasing outside temperature, but errs on the side of providing a little more heat than I think we’ll need. This can be adjusted by simply turning down the set point with the control if need be. The thermostat regulates to 0.1 deg C, which is needed given the fact that very small changes in slab temperature have a significant impact on heat output to the house in heating mode.

If the slab temperature set point is set to a temperature that is lower than the slab actual temperature, the controller closes the valve to the buffer tank and switches the ASHP to cooling mode, to circulate cold water around the slab. This only normally happens when the sun is shining, and the modest power that the ASHP draws in cooling mode is easily provided by the PV array, so this cooling is effectively free. Both the thermostat/controller and the UFH pump turn off overnight to save power, relying on the slab heat capacity to provide any needed overnight heating.

I’ve so far found that running the slab at 19 deg C in cooling mode is fine when it comes to getting rid of excess solar gain, and this temperature minimises the risk of getting condensation on the floor. It also means that the Genvex MVHR can work more effectively at keeping the house cool, as it only has to cool the air from the modest gains that come from the uncooled wall and window cill areas. We’re planning on fitting reflective solar blinds to the East facing windows, and, perhaps, the South facing window in the kitchen, to further reduce solar gain. I may add a covered, glazed roof, walkway along the East side to provide additional sun shading.

Hot water comes from a 260 litre thermal store in the service space. Here’s a schematic of the plumbing to and from from this :

The manifolds for the hot and cold water feeds to each room are next to the thermal store. With hindsight I should have bought manifolds with integral valves and left the pipes coming out of the floor from first fix a bit longer, as that would have made for a neater job. Instead I fitted shut off valves in every pipe and fed the extended pipes up to plain four way manifolds. The access to these is pretty easy, so shutting off any room is pretty straightforward. I have fitted service isolation valves to the cisterns, just in case I need to be able to shut them off independently from the rest of the cold water in those rooms:

On the finishing of things front, all the plumbing and wiring is finished now, the bathrooms, utility room, WC etc are all plumbed and working, with hot and cold water. The borehole problem has been fixed and we have clean water, so it’s just a lot of small, time consuming jobs, to finish off. Here are a few photos of how the bathrooms look, first the main shower room of our bedroom:

Next, the second bathroom off the guest bedroom:

Next door to this, accessed via another door from the spare bedroom is the services area, with the thermal store to the right, the 100 litre pressure vessel for the water supply to the left and the MVHR unit at the back:

To the right of the MVHR, hidden on the wall to the right in the photo above, is the main electrical panel and the pressure vessel for the ASHP and UFH antifreeze, with it’s PRV and fill pipe (it’s filled when needed with a garden sprayer with a modified pipe).

Back there is my home made energy diverter, that senses when the PV system is delivering more power than the house is using and diverts exactly that excess to the immersion heater in the thermal store to heat the hot water. This means that normally all of the hot water comes from excess solar generation, so is free. There is an automatic over ride in the even of the thermal store not being up to temperature. The time switch turns on the immersion, via a thermostat set to 65 deg C at 4 am. If the thermal store hasn’t been heated up enough during the previous day, then the thermostat won’t be satisfied and the time switch will turn the immersion on using full rate electricity to ensure there’s enough hot water for the morning showers. Hopefully this won’t happen too often, but it’s a useful back up to ensure we always have hot water.


 DeeJunFan 05 Sep 2014 06:58 AM :

 You have a home made immersun? While reading this i was thinking about a story i read a little while ago about an italian electrician who set off on a drive into the desert in an old Citroen 2CV. The car broke down and he couldn’t fix it. After a desperate day or so he decided to break the car down and build a motor bike from it.

 Happy as Larry he was free from the desert riding the most mental looking motor bike.

 I’m afraid i would still have an overly warm house and be stuck in the desert.

 Good Job Jeremy


 jsharris 05 Sep 2014 07:08 AM :

 Yes, they are really pretty simple inside, around £20 worth of parts at the most. I couldn’t see the point in spending £200 plus for an Immersun when I could make one for less than a tenth of the cost. All it does is measure the true power being exported from the house (just the same as the Immersun) then regulate the power to the immersion to make sure there’s no power import, without inducing the light flicker that the Mk1 Immersum suffered badly from (I think the new version uses the same technique that mine does, as they brought it out not long after this method was publicised on the web!). There are a lot of home made versions of these devices around now, and even kits available to build them. I used a slightly different design to most, but it functions in the same way.


 ProDave 05 Sep 2014 07:27 AM :

 I never did see the concluding bit to the borehole issues. Did hiring in a firm to clean the hole solve all the issues?


 jsharris 05 Sep 2014 08:25 AM :

 The borehole saga was fixed by the combined effort of the drilling company airlifting the muck and me then lifting the pump up a bit and changing the way the pump feeds the house. One problem was that with the pump running at full speed (it’s a variable speed pump that runs at the speed needed to maintain the head and flow) it was sucking pretty hard whenever the filter went into backwash (it draws around 30 litres a minute in backwash, albeit only for 8 minutes). I installed a 650 litre break tank in the shed and this fills via a servo diaphragm magnetic float valve and a restrictor, with a small (9 litre) pressure vessel and switch to control the borehole pump. This works like a giant cistern, and can fill slowly when the level drops (it fills at around 8 to 10 litres per minute).

 The filtration system and house is fed from a 750 watt pressure set pump, that draws from around 1/3rd of the way up the break tank, via a dip tube with an upward facing intake (to avoid sucking water from the bottom of the tank). This means that I can draw the 250 litres or so of flush water off very quickly without disturbing the borehole. So far this seems to work fine, the borehole delivers clear water when it only has to supply a low flow rate. It may well be able to supply clear water at a much higher rate, as I’ve not tried it, as I’ve now got a system that is fairly simple and works, so I’ll stick with it!

 As far as the house supply is concerned, I now have a higher flow capacity and and pressure, as the pressure set pump is working with a lower overall head difference and is slightly more powerful than the borehole pump. I can have three taps running flat out (after the 3 bar pressure reducing valve) and still maintain between 3 and 5 bar from the pump.


 ProDave 05 Sep 2014 09:28 AM :

 Excellent news.

 you can’t be far off moving in now?


 jsharris 05 Sep 2014 09:34 AM :

 Just the floors to lay in the bedrooms, landing, living room and library, then fit the skirting and architrave, make and fit the doors to the eaves access, fit a fitted wardrobe in the main bedroom, fit the internal window cills to all the windows except the one in the kitchen (which are already done), touch up some of the paintwork, finish off the required landscaping to keep the planners happy and we’re ready to go (I think…………).


 bitpipe 05 Sep 2014 10:43 AM :

 So the big question is what do you have planned to fill your time once it’s all done 



05 Sep 2014 02:53 PM:

Travel the country fitting low energy UFH controls you have made….

Install ASHP for people not wanting to pay massively inflated charges and don’t want thr RHI

Comission MVHR units that have been self installed….

Or set up a Passive House consultancy and do all of the above


 ProDave 05 Sep 2014 04:35 PM:

 Hire out all your home made test kit to other self builders for reasonable rates to supplement your income.

 Sit in your garden and smoke your pipe and cut the grass every other day.


 TerryE 05 Sep 2014 04:43 PM:

 Jeremy, to quote Jan’s comment of 30secs ago: “this is very useful, isn’t it”. So very timely and thanks from us both.

 I am in catch up mode on my blog entries at the moment, but one of the things that I am doing is a second-pass review of all of the relevant PV and UFL topics, because Jan and I are in the process of completely rethinking our heating approach: we have pretty much swung around 180 deg on our heating approach: (i) Add ASHP-based UFH for overall temperature control; (ii) abandon the Genvax and replace by a good std MHVR unit; (iii) integrate PV into our roof and our heating strategy.

 This is all part of a new and separate thread really, but one 20:20 hindisght Q: If you had got the thermals and MVHR vent placement optimum, would you even bother with the Genvax? Does it add enough to the overall design to justify its inclusion?


 stones 05 Sep 2014 05:34 PM:


 Very informative.

 I know you have discussed other options you would now consider with hindsight.

 Assuming you split the DHW and UFH so that you had no buffer / thermosyphon, could you complete your UFH heating / cooling system entirely with off the shelf items or would you still need to custom fabricate certain parts?

 Regarding condensation, have you experienced any at all when cooling the slab?

 What to do next – finish off inside then take a well earned break, ready to tackle the garden next spring!



 jsharris 05 Sep 2014 06:01 PM:

 I’m very definitely going to have a break from anything related to building a house for a while!

 Happy to loan out the air flow meter, but it is now out of calibration (I bought it second hand but it was still just in cal), so I’m not sure how that would effect a commissioning report for BC.

 With hindsight I’d not have fitted the Genvex, but would have gone for a much cheaper (and smaller/lighter) unit. I might well have added a cheap £500 split air to air heat pump with the internal unit up in the hall roof, very high up, though.

 I’m pretty sure that control could be with standard off the shelf parts. The company I bought the programmable humidistat from do a similar temperature controller, and that looks as if it would do the job of turning the ASHP on and off with fine enough control to regulate the slab temperature. All that would then be needed would be a switch to select heating/cooling which would be easy, as it’s just closing a pair of no-volt contacts. The circulating pump could be just as I have it, on an off-the-shelf time switch.

 I’ve seen no sign of any condensation on the floor at all, and as a large part of it is travertine I think if I was going to get it I would be able to see it. The surface of the floor is always around half a degree or so warmer than the slab, according to both my IR thermometer and a small flat plate sensor I made up to rest on the floor surface, and I have the floor set so the slab is at 19 deg C in cooling mode, so around 19.5 deg on the surface, so there’s virtually no realistic prospect of the humidity being high enough to cause condensation, I think.


 declan52 05 Sep 2014 07:28 PM:

 gd tip for the architrave the guy doing mine was using a glue that kitchen fitters use for gluing mitred corners of cornice. He laid the three pieces on the floor glued them up, waited a min then lifted them up all stuck together and nailed it home made it look so easy. It was something like this stuff. Will work for all of your external cuts of skirting to. Never seen it done like this before, maybe i need to get out a bit more !!!



 jsharris 05 Sep 2014 07:42 PM:

 Brilliant tip, Declan, pure gold! I wasn’t looking forward to fitting the architrave (or the skirting) but this stuff looks like it might make the job a heck of a lot easier, especially as I’ll be working on my own.


 joiner 06 Sep 2014 07:48 AM :

 J, there are companies out there copying and pasting all this stuff into the technical manuals of the whole-house systems you’ve designed and which they are now selling for mega£.

 Respect, my man!


 jsharris 06 Sep 2014 07:59 AM :


 One company has emailed me and asked me about the system and if they can use some of the ideas and I said they could. Another is using some of the things I’ve found out and slightly modifying the way they are looking at passive house heating and cooling, again with my blessing.

 The main thing is that the information on what works and what doesn’t work (or isn’t really needed) be available to all, so people can better understand if they are getting good advice. That alone should limit the potential for people to be ripped off, just by keeping all the information out in the open.


 joiner 06 Sep 2014 11:28 AM :

 Ah, the original spirit of the CAT before it went ‘commercial’! Went there twice for courses and the first time was when it was still ragged-ass, hands-on, the second time was like having gone through a culture-warp, hardly a calloused hand or broken fingernail anywhere. Although you still had to go down the road to get a bacon sandwich.

 Open source rules, OK!

 Just waiting for “them” to appear on here offering “advice”.


 jsharris 06 Sep 2014 12:06 PM:

 I went to CAT in the late 70’s and it was just as you say, a sort of knit-your-own yoghurt place, but I’ve not been back since. It’s sad if it’s just become a haven for consultants, though, a bit like the AECB, perhaps.

 We do lack a source of reliable, free information on all this stuff, as it’s a complete minefield to try and make sense of. My background is in science and technology, so I had a head start when it came to trying to work out what we needed, but even I’ve made some serious errors, and spent a fair bit of money that I didn’t need to, just because I struggled to understand quite what the house real heating and cooling needs were. I’d not thought for one moment that a house in South West England would need cooling more than heating, but clearly ours does. I worried a lot about heating, when I doubt that we’ll really need much, if any, heating at all.

 Far too many people have taken a sales pitch at face value and ended up with systems that don’t do what they want, or which cost a lot of money to run, we’ve seen several examples on this forum of people with UFH and ASHPs that fail to keep their houses warm and cost a fortune to run, for example. There are very, very few people in the renewables/low energy sector that I’d trust, as the good guys are massively outnumbered by the snake oil salespeople.

 I’m usually reasonably good at spotting those peddling snake oil here, but I think we have to accept that for many good, well experienced, heating engineers the concept of a low, or zero, energy house is something that they just haven’t come across before, so they will, very understandably, find much of the stuff about low energy heating pretty challenging to get their head around. Much like my constant worry that I wasn’t going to be able to adequately heat our new house in winter, they will want to err on the side of providing more heating capability than required. This technique works fine with an older house, because if it accidentally overheats it will cool down very quickly. It doesn’t work with a very low heat loss house though, as if that overheats it takes days to cool down.

 What’s needed is two things, IMHO. Firstly, free and easy access to information in a form that ordinary consumers and self-builders can really understand. Secondly, tradespeople and systems designers who can have ready access to free information, with no commercial interest from a particular manufacturer, as to how to approach designing and installing a system that suits a particular clients needs. This latter point is of particular relevance to small business, who may not have the time or money to sign up to training or awareness sessions run by other bodies, like CAT or the AECB.

 The fact that this forum is free from commercial influence and free from any form of editorial censorship means we can use it to help people out. Hopefully this will produce a sort of chain reaction, where one persons experience informs ten others, who then go on to each inform ten more. In this way I think we can, in a small way, help self-builders and renovators make informed decisions.


 stones 06 Sep 2014 04:28 PM:

 “jsharris, on 06 September 2014 – 07:59 AM, said:


One company has emailed me and asked me about the system and if they can use some of the ideas and I said they could. Another is using some of the things I’ve found out and slightly modifying the way they are looking at passive house heating and cooling, again with my blessing.

The main thing is that the information on what works and what doesn’t work (or isn’t really needed) be available to all, so people can better understand if they are getting good advice. That alone should limit the potential for people to be ripped off, just by keeping all the information out in the open.”

 It’s refreshing to hear that at least some companies have formally approached you and sought permission. I hope they are sending a bottle or two to you in thanks! I really do take my hat of to people with detailed knowledge who are willing and happy to give of their advice for free / on an open source basis. Having been on the receiving end of what I certainly believe to be snake oil salesmen and (razor) sharp practice, I’m certainly grateful for the help and advice I have had.



 jsharris 06 Sep 2014 04:51 PM:

 I think that it’s also a pretty good sales tactic for those in the business of selling low energy houses and associated systems. 

Sadly I’ve had a poor experience with too many companies now. I well remember an encounter at a show, and a subsequent lengthy email exchange with one company who were supplying a “thermodynamic system”. At the time I was very interested in one as a DHW system (I still am, in fact). The salesman at the show was a reasonable enough chap, but clearly hadn’t got any detailed technical understanding of the product he had on show at all. He did have the sense to realise this and gave me their technical guys details. I then spent the next ten days exchanging emails and trying to get some really basic information from them, like what the measured COP was for specific temperature differentials. This is all standard stuff, that any heat pump supplier should publish. Despite all my efforts the best I could get from them was statements like “we’ve installed dozens of systems and all our customers are happy”, or “we’ve got letters we can show you from customers showing how much their bills have reduced”. All I wanted was some basic test data, like “what’s the COP when it’s 5 deg C outside and the unit is heating water to 40 deg C?”. In the end I gave up trying to get anything out them at all, as they clearly hadn’t got a clue about the thing they were selling.

 This is a shame, as I still have a feeling that a single panel direct heat exchange air source heat pump like the “thermodynamic panel” system is a viable way to provide hot water, and I have the perfect space for one on the East facing gable end of our house, where it’d get the morning sun all year around, just when we need a hot water boost. Without hard data on its true performance though I’m not going to buy one.






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