Zehnder Q350 + ComfoPost CW12

[BartW]

Hi,

I am having the Q350 and Comfo Post delivered for our self build, and while the schematics seem plain and simple:

 

 

 

 

 

I wonder how to best connect and control the Comfo Post here.

 

The heating system will be driven by ASHP (Vaillant Aero Therm Plus with UniTower) with a cooling option (resistor).

 

How do I best control the flow through the ComfoPost:

 

- as it happens I am siting a UFH manifold in the loft right next to where this unit is going. Could it be a good idea to either tap into the supply pipe to the manifold

- or perhaps add a separate zone / port to the manifold and run off of that? The downside is that if this local manifold gets no call for heat "pump operation" there would be no flow at all regardless of whether the zone be open.

 

The benefit of the latter would be ability to open and close the circuit. Also the loop would be super short and would run through a pump that would be fairly local there. Or I could leave this port "always open" and assume that when I run heating, I would automatically have demand for additional heat through the vents. In reverse, i.e. for cold air the same would happen with cold air being added in. 

 

 

 

Otherwise, how would one logically control this above scenario?

 

Thanks!

 

Bart

 

 

 

 

 

 

 

 

 

 

 

[Dan F]

3 hours ago, BartW said:

How do I best control the flow through the ComfoPost:

 

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.

 

3 hours ago, BartW said:

Could it be a good idea to either tap into the supply pipe to the manifold

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? 

 

 

[BartW]

5 minutes ago, Dan F said:

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? 

 

 

 

Hi,

So, I am doing the whole thing myself. Design included.

 

Yes, I saw Vaillant list a part that attaches directly to UniTower, and that is designed for totally separate zoning. I think it comes with a built-in own pump too. One of these? (part ending 507,8,9). 

 

 

As for the CW12 being big, it was not flagged up to me that it was going to be too big for the unit. Paul Heat Recovery have done the design for the MVHR on this one.

 

 

 

 

 

 

 

 

[Dan F]

9 minutes ago, BartW said:

As for the CW12 being big, it was not flagged up to me that it was going to be too big for the unit. Paul Heat Recovery have done the design for the MVHR on this one.

 

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?

 

9 minutes ago, BartW said:

So, I am doing the whole thing myself. Design included.

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.

 

Edited January 5, 2023 by Dan F

[BartW]

2 minutes ago, Dan F said:

11 minutes ago, BartW said:

 

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?

 

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?

Yes, all ducts are to be insulated. 
 

I need to check the calcs that PHR provided, but the assumption was the bigger the CW unit the more heat it was going to put through regardless of flow. 
 

Yes, I was not expecting for Comfopost to provide too much of a difference, although I was hoping it would “help”. 
 

am I being naive?

[Dan F]

33 minutes ago, BartW said:

I need to check the calcs that PHR provided, but the assumption was the bigger the CW unit the more heat it was going to put through regardless of flow. 

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!

 

33 minutes ago, BartW said:

Yes, I was not expecting for Comfopost to provide too much of a difference, although I was hoping it would “help”. 
 

am I being naive?

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.

 

 

 

Edited January 5, 2023 by Dan F

[BartW]

Thanks Dan 

 

Sounds like you have been there and done that. I will quiz the supplier tomorrow and maybe change that bit on the order or ditch completely…

[Dan F]

4 minutes ago, BartW said:

Thanks Dan 

 

Sounds like you have been there and done that. I will quiz the supplier tomorrow and maybe change that bit on the order or ditch completely…

 

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?

[BartW]

6 hours ago, Dan F said:

 

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?

Hi,

yes ufh for cooling too. Comfopost for the whole system, both heat as well as cool. 
 

flows attached. 

[Dan F]

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?

Edited January 5, 2023 by Dan F

[BartW]

Hi,

This is UFH + Comfopost on all three floors.

 

Flow rates, let's see...

 

 

 

 

 

 

[JohnMo]

Just been looking at this out of interest, just looked at the datasheets for Comfopost

 

Things noted 

The smallest unit is the one to go for your 217m3/h is mid range in the datasheet. 

Requires some high water flow temps to a get a small heat output.  Could lead to dreadful CoP for a heat pump

Water flow rate is 10L/min, which will be too low for a heat pump if this is the only use for the water.  So a buffer would be required

The heat exchanger differential temperature is very low again rubbish for a heat pump

 

You could get A2A heat pump for the same/less and it would do a better job

[BartW]

I would rather ditch the comfo post completely if it is likely to make zero difference, make CoP shit and cost extra gubbins to make it work...

[Dan F]

5 hours ago, JohnMo said:

Things noted 

The smallest unit is the one to go for your 217m3/h is mid range in the datasheet. 

Requires some high water flow temps to a get a small heat output.  Could lead to dreadful CoP for a heat pump

Water flow rate is 10L/min, which will be too low for a heat pump if this is the only use for the water.  So a buffer would be required

The heat exchanger differential temperature is very low again rubbish for a heat pump

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.

[markharro]

Interesting to read this given that I was planning the same kit as the OP. I had asked Paul to requote adding the Comfopost from memory at the height of last summer I think. My hazy recollection of the logic was to give some cooling ability during the hottest weather. This would then add to running the Vaillant ASHP we plan to get on reverse. Having read this thread I am also wondering if it is worth the extra cost and hassle!?

[BartW]

3 hours ago, markharro said:

Interesting to read this given that I was planning the same kit as the OP. I had asked Paul to requote adding the Comfopost from memory at the height of last summer I think. My hazy recollection of the logic was to give some cooling ability during the hottest weather. This would then add to running the Vaillant ASHP we plan to get on reverse. Having read this thread I am also wondering if it is worth the extra cost and hassle!?

That was exactly me. Same Summer!

 

I have my order pid and ready to come to me, but sounds like I will be cancelling the cw12 and the duct wraps. 

[Dan F]

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

[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?

 

 

[Dan F]

On 05/01/2023 at 12:28, BartW said:

Hi,

This is UFH + Comfopost on all three floors.

 

Flow rates, let's see...

 

 

 

 

 

Given 217m3/h, the best (theoretical) outputs you can expect are going to be:

- Heating 2.3kW            (assuming 50% RH, 21 inside temperature, -2C outside temperature, 90% efficient MVHR and 55C ASHP flow rate)

- Heating 1.6kW             (assuming 50% RH, 21 inside temperature,  7C outside temperature, 90% efficient MVHR and 45C ASHP flow rate)

- Cooling 1kW sensible (assuming 50% RH, 21 inside temperature, 35C outside temperature and 90% efficient MVHR, and 7C ASHP flow rate).  You'll also get dehumification on top of this.

 

So heating may be somewhat significant, depending on your heat loss, but it's an inefficient way of heating that won't get you same COP vs UFH; with my ASHP it means 2.4 COP (@-2C) vs. 3.6).  The (sensible) cooling output is low though.  It's impotant to look at these numbers within the context of you heating/cooling load and other emitters you have planned though.

 

It would worth getting CW8 for these flow rates, and not the CW6, so you are at the low end of the recommended flow rates. But, there is no reason to get CW10/CW12 unless you increase these flow rates a fair amount, which would probably mean a larger MVHR unit too.  (CW10/CW12 do have slightly reduced pressure loss, but this is minimal)

[Andehh]

We considered one for a very short amount of time... Then went down the A2A route. Just because massively improved performance for a reasonable (but not massive) cost in the rooms where it mattered. Rest of the house will be fans and ASHP cooling. 

[Dan F]

1 hour ago, Andehh said:

We considered one for a very short amount of time... Then went down the A2A route. Just because massively improved performance for a reasonable (but not massive) cost in the rooms where it mattered. Rest of the house will be fans and ASHP cooling. 

Did you not consider fancoils using ASHP, instead of A2A?

 

1 hour ago, Andehh said:

Rest of the house will be fans and ASHP cooling. 

Fancoils you mean?  No UFH cooling?

[BartW]

Thanks for the replies gents. 
 

I am due to take a delivery of the equipment next week, so will try to cancel the CW12 altogether. I feel I should have researched this in more detail a lot earlier. 
 

thankfully, my “smart home quest” helped rule this out, so thanks again to all involved!

 

time to move on to the next query (surely lurking somewhere in my head)

 

[Mr Blobby]

7 hours ago, BartW said:

I am due to take a delivery of the equipment next week, so will try to cancel the CW12 altogether. I feel I should have researched this in more detail a lot earlier. 
 

 

 

Our M and E guys laughed at my suggestions to install UFH cooling and fancoils.  They insisted comfoposts were the only option despite my objections that the heat capacity of air and flow rates would be insufficient to make much impact.

 

Not installing comfoposts.  M and E guys are history.  UFH cooling and blinds on the big windows.  No heating upstairs.

 

 

 

[Nick Laslett]

Hello @Dan F, any advice on the ComfoPost would be appreciated. I’m just interested in using the ComfoPost for cooling, combined with the Upstairs and Downstairs UFH circuits. All the south facing windows have 70/30 solar control coating. 
 

My current simple plan was to tee off from the 28mm UFH supply and return pipes, with 15mm pipes going to and from the ComfoPost, with a flow regulator. In heating season the 35° C water temp would not do much, if anything. For cooling in the summer running 7° C water through the UFH and the ComfoPost would hopefully take the edge of the heat in the house. The PV should power the ASHP for this purpose in the summer.  The supply ducts have been insulated. 
 

I was looking at the ComfoClime 36, but the ComfoPost is a lot cheaper, and apparently more effective. 
 

Any advice would be much appreciated. 
 

@markharro, did you go ahead with the ComfoPost?
 

 

[Dan F]

@Nick Laslett I wouldn't do it again, instead I'd put fan coils in.   Compost for the whole house, or just the first floor?  What about easterly/westerly windows, any shading/overheads?