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Hi Guys
A belated thanks for the input here. We didn't manage to find a suitable installation to visit, but have been allowed some fluorescents anyway!
Nick, those fittings you linked to are brilliant and we have pinched the idea and developed it somewhat – the pair of buildings in question are craft workshops, one a pottery and one a weavery, and the idea is that we have a fitting into which the craftspeople can place items of their work – thin porcelain panels in the pottery and a frame with fabric stretched over in the weavery (definitely no tungsten bulbs allowed in the latter!) Should look really good, and the clients love the idea.
Cheers
Toby
Aren't all heating systems thermodynamic?!
I assume you're referring to the Heat pump systems employing a solar collector as the evaporator. As far as I can tell, these offer all of the disadvantages of ASHP's and solar thermal, with none of the benefits. The evaporator is poorly optimised for absorbing heat from the air, so doesn't work well when there's no sun, when the radiant sky temperature is low. When it is sunny, then your conventional solar thermal is probably a better bet for DHW, and if your passive design is half decent you won't need much heat anyway…
Hi Mark
Interesting questions. For context, The price of a Grundfos Alpha 2 (15-50) looks to be about £90 cheapest retail I can see on google, whereas the 'standard' UPS 15-50 is about £60. We often end up speccing these on houses simply because there's not anything out there that's smaller.
We are starting to put monitoring kit in our projects so I hope in due course I'll be able to give some firm ish figures on this but here's some food for thought in the meantime.
The length of the heating season in PHPP for the south England weather data file is 205 days (I've just been playing with this in some detail for my PH conf paper!)- however that's not necessarily the same as the number of days there is call for heat. Compared to the SAP assumption that's a little less than 10 hours a day which doesn't seem unreasonable (three hours in the AM and seven in the evening…). Not sure if there is such a defined heating season in SAP. Let's go with 2000 run hours for now.
I'm about to make a fairly drastic assumption in order to keep this 'back of the envelope' style: say that the amount of power used by the pump ramps up and down linearly from the beginning of the heating season to the peak and back down again. The minimum rating is say 5W, and the peak is 65W, so if you drew a graph of the power demand against time in heating hours you have a 'childs house' profile (rectangle on the bottom, triangle on the top.) The rectangle is 2000h wide and 5W tall giving 10 kWh, and the triangle is 60 W tall and 2000h wide, giving 60kWh, total 70kWh. A constant speed pump would have consumed 2000h times 65W i.e. 130kWh. On a say 100m2 build, that happens to be exactly 1% of your PE criterion – not earth shattering savings…
Difference of 60kWh @13p/kWh is £7.80, simple payback of 3.8 years – not bad, if my rudimentary assumption is anywhere near accurate. As you highlight, this annual saving reduces as you shorten the heating season, but on the other hand it might be more likely to be running at part load…
However, the pump will also encourage your boiler to condense more because at part load, it pumps less water for the same heat output, so the return temperature will be lower. This is more difficult to put a figure on, but I wouldn't be surprised if it added a few % points to the seasonal efficiency of a typical system. I would also wonder whether the TRV's get exercised more and therefore last longer – but I really don't know about that.
I haven't seen any domestic style boilers with a variable speed pump in them, I haven't tried asking a manufacturer if they can supply a unit with a specific pump in it.
A couple of caveats; one is that as you reduce the pressure in the flow the valve authorities can start to look poor on some systems (usually only a serious issue on bigger systems) but this can be solved by appropriate use of differential pressure valves, but of course you'll be engaging an M&E consultant to get that bit right for you ;0)
Finally, and probably most likely to be of concern, a priority DHW circuit has the potential to cause issues if the pump is in proportional pressure mode (constant pressure mode, which is energy saving but not as good as proportional pressure); if there's a lot of back pressure in the circuit and coil the pump will ramp back, thinking that all the rads have suddenly shut down, reducing your flow and meaning your cylinder heats up slowly. I might actually mention this to Grundfos (other pumps are available…), because it would not be beyond the wit of man to connect a control signal from the DHW engage to a bit of logic on an inverter to override the speed control.
Hi David
I did ask, and he specifically mentioned flicker as a concern, but other things he said led me to think other factors may be contributing to his resistance. Pink Tesco lights may have contributed, and I'm sure we've all experienced a bad, old-fashioned lighting design that would put anyone off fluorescents (my gym has a fitting in the gents that sounds like a drunk blacksmith hitting an anvil while it tries to strike the arc, and then sounds like a very angry, very loud bee!).
LEDs are a possibility (application is a weaving and craft workshop), but as you say, there is a relatively tight budget and it's not always easy to get a nice ambient element to schemes with LEDs.
Hence hoping to be able to enlighten him to the performance possible with modern systems!
Yes, correct – consider it as one building with four dwellings within it. There's a box on the verification page indicating number of dwelling units that will need to be 4.
Sue Roaf are you listening?!
I can't imagine the K value of render with EXP beads mixed in will be very good, and if in thin layers as you suggest (25mm?) it's not going to improve matters very much, so bang:buck ratio will be poor and people will be left wondering why they spent their money, maybe giving you hassle for recommending it.
There really is no substitute for a thick (and continuous) layer of something fluffy when it comes to conductive losses! I forsee this being a bone of contention in the not too distant future, when we are forced to decide between keeping our pretty, maybe listed facades and (proper) EWI.
Got a project on site right now where they bit the bullet and built a wooden frame around the house (solid wall) to create a 200mm void which will be filled with mineral wool, finished with wood wool boards and render. Not trivial or cheap, but will transform the thermal performance of the house.
There are a lot of issues wrapped up in here!
You man is right that oversized rads will operate at a lower temp for the same heat output and therefore *can, potentially* reduce the operating temperature of the system, which *can* inrease the efficiency of boilers (and especially heat pumps). However, this will probably require upgraded controls possibly including a variable speed pump… When you take all of this into acount I would question the economics of upsizing rads being a good saver – possible but not as straight forward as your chap implies.
Also note that the boiler won't be working any harder or, erm… lighter – it will be supplying the amount of heat demanded by the rads at a generally lower temperature.
Mark, I'd probably advocate them strongly if I was selling them 😉 but that's not to say they aren't good, I'd just like an independent opinion if there's one to be had.
Dave: “4 electronic thermostats in the 4 airstreams are connected to the electronic Brain which controls the motor speeds, maintaining a high efficiency when the wind blows or a door is opened.” from the viking website http://www.viking-house.co.uk/fine-wire-hrv.html
I agree with your point about HX efficiency and ducting but in this case we have 1 room on each floor plus WC, possibly WC/shower on ground, and bathroom on 1st. Am considering a WiFi for each of the main spaces, and maybe one of those through the wall HR units that are designed as drop in replacements for standard extracts for the wetrooms. It just seemd a sensible alternative to full MVHR given the size and layout, and that the bedsit and office are likely to be occupied at almost exactly opposite times.
There's also a chap on the navitron forum that's acquired the bare HX and has been experimenting with incorporating it into a ducted system:
http://www.navitron.org.uk/forum/index.php/topic,15839.msg177733/topicseen.html#msg177733Hi Nick
Ha, designing a PH School – I wish! I meant us as designers who are members of the “School of PH”. But the point is worth making, that at larger scales, the flexibility and range of kit is much greater than the choice of domestic scale 'boxes'.
Totally agree on the kitchen issue, I simply don't believe these systems that claim they can handle air from an extract hood, which is a shame as there's so much heat to be recovered from that hot, wet air!
Thanks guys, nice to hear I'm not missing something!
I've re-read the article but it's even more baffling now, it's mixing up a lot of issues.
On the other hand, if these complaints are genuinely arrising, what should we, as designers of the PH school, be doing better? No smoke without fire (an unfortunate analogy).
I am aware of some pretty poor systems (from a design point of view) and have narrowly avoided one or two of these on projects where we were borught in a bit late. Is it possible to out-compete the bargain-basement design-install outfits, or is there insufficient public appreciation of what we do?
Also the range of MVHR available is not great, controls and ability to do mixed-mode being two aspects that I've had painful experience with, at a domestic scale at least. How can we persuade manufacturers to raise their game?
An open loop system will normally have two boreholes, one extract and one injection. The HP pumps ground water out from one borehole, extracts some heat from it, then squirts it back into the second borehole – there is no waste as such, you aren't supplying the open system with water from your taps!
Closed loop systems are much more common, I believe you need quite specific ground conditions for an open loop system. We have recently put in a surface water heat pump and the supply/install co didn't even consider open-loop, so it's basically a GSHP slinky pinned to the bottom of a marina.
I have no evidence but suspect open loop systems are no less efficient than closed. The cruical parameter is the temperature of your source, and if you have a high enough water table with enough sub-terrainian flow to justify open loop, a borehole closed loop will also recieve these benefits. Technically, I'd have reservations about sucking up god knows what, which 99.9% of the time will be dealt with by filters but… Closed loop avoids this issue.
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