Dan F

Comfopost does so something, don't get me wrong. But it's important to understand (calculate) your heating/cooling demand and the power output you will achieve from comfopost otherwise you are likely to spend money, be dissapaointed and it potentially be too late to employ a different strategy. We did have the calcuations done, but I think there was some incorrect assumptions made in the calculations unfortunately. My advice: - Do not assume the figures in the datasheet are what you'll get as they make assumptions about MVHR output (comfopost input) air temperature which are unlikely to be true in real life. - Consider that that the kW output from Comfopost is not directly comparable with kW output from any other emitters because the input air temperature is lower than room temperature (this is important given if you need to run boost which will increase MVHR losses). - Do not assume that a larger Comfopost unit will always heat/cool more, it won't! The main limitation is air volume, not the exchanger. - Consider that you'll need to run at less efficient flow temperatures to get any noticeable heating output. - Consider that you'll need to run MVHR at boost (or preferably even higher than boost) to get any any noticeable heating output and that this may require specifiying a large MVHR than you would use otherwise). - Don't plan to use Comfopost for cooling unless you have have fully controllable solar gain (e.g. automated external blinds), have calculated your cooling load as very low, and don't expect to be able to actively cool the house, but rather just stop temperature rising. - If using Comfopost for 1st floor only, consider that boosting MVHR will cool/heat the ground floor slightly (not an issue if you have UFH on GF, but it represent increased MVHR looses) - Know that you need to insulate ducting. Anyone quoting for Comfopost should really be doing the calcuations so you know what ouputs to expect from it given MVHR design. Do Paul not provide anything in this regard? What is there justification for quoting for oversized CW12 with Q350 MVHR?

How did you deal with G99 with this?

Agree, there are more varibales here than just the existenace of the buffer. One of these being no use of internal temperature sensor of thermostat in system 2.

This is a good reference top: https://www.greenbuildingstore.co.uk/can-an-mvhr-system-be-used-for-cooling/

Page 56-59 talks about pros/cons of 2,3 and 4 port buffers in heat-pump system. https://www.caleffi.com/sites/default/files/file/idronics_27_na.pdf?fbclid=IwAR0KGbAXmvSRXNdyevldqeUhD6u7iF4RKWaI5Cxq6BNXKbYx-U19wKJ1_5E

If you only have a single heating zone which has large enough capacity for desfrost and is always open, the best approach is no buffer at all surely, not a 2-port buffer. Mixing may decrease efficiency in some scenarios, but energy doesn't get lost via mixing. I don't see it as inevitable, I think it depends on exact scenario and flow rates and the ASHP control system. Mixing doesn't produce energy loss, so at worst it makes the ASHP less efficient via use of a higher flow temperature (but this is turn also depends on what temp sensors and control system the ASHP is using) BTW, In theory 3-port buffers are better than 2-port.

This article is good explaining the difference between 2-port and 4-port configurations: https://www.pmmag.com/articles/100544-the-finer-points-of-applying-a-2-pipe-buffer-tank If buffer mixing is an issue and how much this impacts efficiency will be implementation specific. My ASHP for example (Vaillant), doesn't adjust flow rate in partial-load scenarios but rather maintains a constant flow rate. I also have mixed circuits which means that the flow rate out of the 4-port buffer is actively reduced when heating load is low. I'm not sure exactly how it behaves in practice, but I'm pretty sure it doesn't follow the scenario 3 mixing explaination. The other difference between scenario 2 and 3 is that scenario 2, which may be more significant, is that system 2 is using what vaillant call "room mod: inactive" and system 3 is using what vaillant call "room mod: active". This will effect how the weather compensation is working and in turn the flow temperature.

OK. So, what explains why the same ASHP, with in theory the same weather compensation config, required 40C flow instead of 35C flow when a buffer is used. This can't be buffer losses.

I only have one buffer. The heating circuits (for UFH and ComfoPost) are both mixed with indpendant temp control.

I can't see why an insulated buffer (even if it has some losses) would require 40C flow vs. 35C, there is something else going on here. not just the buffer IMO. Potentially the post buffer pump is running too fast/slow and delta-t isn't optimal?

Also the quoted power outputs assume incoming air temperature that is not realistic when you have an MVHR in front of it. 28C in summer, 17C in winter.

This is very interesting and maybe even deservices it's own thread. I understand when system 1 is bad, but the difference between system 2 and 3 I struggle to understand: - There is clearly a slightly loss of efficient when the system starts (and I know Vaillant VF1 sensor makes this worse). - But, once things stablize scenario 2 is using 40C flow temp and scenario 3 uses 35C flow temp for some reason. The only reason I can think this is happening though, is because of an insufficient flow rate on the other side of the buffer tank and the delta-t being too high. If you use a correctly size pump and tune things correctly (or use a self-balancing actuactors), I can't see why system 3 would need higher flow temperature or perform worth than system 2. The author states that "the second test also showed drop in performance and high running costs due to the influence of the buffer tank and the secondary circulator working against heat pump’s controller which was maintaining steady state output and performance" but doesn't go on to explain how he beleives the buffer tank and secondary circulator working against heat pump. What do others understand?

I paid 8-10 for these I thnk. You are right though, Loxone prices aren't cheap and you can get these cheaper elsewhere. One of the reasons I paid extra from the Loxone was simply because they had 2.5m cable on them, which is long enough to put a sensor in the slab in a largish room and then hide connections in studwork, others I saw at the time were less than 1m. Looking today though, there seems to be a cheap supplier on amazon with good reviews and 3m leads: https://www.amazon.co.uk/AZDelivery-Stainless-Temperature-Waterproof-Raspberry/dp/B07KNQVWV2/?th=1

I used these and currently have around 20 on single 1-wire extension. https://shop.loxone.com/enuk/1-wire-temperature-probe.html

So ground floor is UFH+ComfoPost and fist-floor is just ComfoPost? Any idea if those value are normal flow rates or boost rates? Did they calculate any heating/cooling power output from Comfopost?

Get you design flow rates and share these. Also, how were you planning to use ComfoPost? - Whole house or just first-floor. - Heating, cooling or both? Will you be cooling UFH too?

£70 and it's a whole computer running linux. Mine does all my DALI lighting too. They aren't that easy to get hold of currently thats only slight issue, but I'm sure you'll find stock somewhere before you need it. https://thepihut.com/collections/raspberry-pi-kits-and-bundles/products/raspberry-pi-starter-kit

Daisy-chain shielded CAT6/CAT7 between all locations you need 1-wire temperature sensors and make sure you put these sensors in slab, screed or under tiles as required. https://www.loxone.com/enen/kb/wiring-1-wire-devices/

It might make sense to go up one size to ensure you get the best performance, but a bigger Comfopost does not mean more heating/cooling power!! Assuming the heat-exchanger is large enough, power is a function of water temperature, water flow rate, air flow rate and input (from MVHR) air temperature. So even if you boost flow rate is almost 350m3/h, once you go beyond the CW8 a larger heat exchanger makes no difference as it won't change any of the variables. Assuming water temperature is 7C (and you don't control air temperature), the easiest thing you can do to get more cooling/heating power is buy a bigger MVHR to push more air through the system! Probably, yes. I was fairly naive before too! I do get some noticeable heating from our Comfopost but the output is low (1.5kW) even with a Q600 on boost and with an (inefficient) high flow temperatures (e.g. 45-55C). It's good as a backup solution or for taking off the chill, but if I was doing this again and wanted an efficient approach to ensuring the first-floor wasn't up to 3C less than ground floor on the coldest days of the year, then I would consider using another heating source on first-floor. Cooling output is significnatly less and has no noticeable impact in reducing temperature of the first floor, even though we have passivehaus spec insulation and windows and have automated external shutters on all windows. To be fair, I'm sure it did do something and stopped first-floor heating up quite as which when MVHR was outputting 25C in the heat-wave, but it couldn't actively reduce the first-floor temperature.

Well if you are controlling UFH, you need temperature sensor in the floor, not a wall sensor, so I wouldn't rely on the touch switch sensors. Relay is simply on off yes. Just need to controller with temp input, target temp and hysteresis (there are muliptle ways of doing this in Loxone) and then output is digital 0 or 1 to relay.

Yes, bascially everything you can do via the app, plus all the stats you can get from the app. You do need to set up Loxberry and MQTT etc. but it's a one-time setup.

CW12 is designed for 550 m3/h->. Max airflow for Q350 is 350 m3/h, but if you are using this unit then I assume you design flow rate is actually more like 250m3/h? There is an argument to oversize ComfoPost somewhat, but in this scenario IMO CW12 is just bigger and more money and not going to improve heating/cooling power. You know to expect very little heating power from Comfopost and significanlty less cooling power from Comfopost, right? Also, that all ducting shoud be insulated? Did Paul calculate and tell you what kW heating/cooling power you'll get from the system? I suggest downloading all the manuals, including the sensoComfort manual which details the use of VR71, and reading them front to back. There are cost savings with doing this yourself of course, but there are also risks. Not clear what is in those kits in parts list.

If you are using Loxone, why not use the 1-wire sensors? Then it's just a case of using a simple controler with configured hysteresis to turn UFH on/off. This is better than simple on/off. If you don't want to use 1-wire sensor than something with a linear 1-10v output would be easy to integrate via an analog input. You then simply map this to the temperature range e.g. 1v=0C, 10v=100C and within loxone you work with the temperature. Digital inputs a 0/1 so aren't suitable for temperature sensor, you'd need an external thermostat with a digital output.

Another alternative is homeassisant which has a plugin and then bridge to loxone. Yes you need a raspberry pi, but you can do a lot of other stuff with Loxberry too and it seems you are planning to buy/install the Lan C box anyway. If you want to avoid raspberry pi then by all means use the options box (it looks like it costs a lot more than a raspberry pi though) just need to note that I think it's mostly inputs, you aren't going to get any stats (temp, humidy, fan speed) from it I don't think. You might also want to check that you can use both LAN C and Option Box at the same time. Lastly you can use the ComfoConnect KNX and Loxone KNX extension but then is more costly and complex, especially if not using KNX for anything else.

You can use a dedicated mixed Vaillant circuit for Comfopost if you want which will allow you to control circuit temperature independantly. Alternatively, if comfopost circuit will always be the hottest/coldest circuit you can just use a circuit with a zone-valve but not mixer or temp sensors. You don't want to tap off the UFH manifold. UFH will need to run at different temperature. Need to be prior to UFH mixer. Do you have someone designing and installing ASHP? Once set up as two circuits you can contol them UFH and Comfopost as seperate zones with different controllers (which as as zone thermostats). The CW12 is a big unit, especially given the small Zehender Q350! What is the thinking?