Heating & DHW System for a passive house

BigGeorge

Am looking for feedback /opinions on the following suggested heat/DHW system for a passive house, in particular around complexity, effectiveness or cost would be great:

8-10sqm, solar thermal array on south facing roof
Large capacity HW tank in the plant room, 750-1000lt, for DHW & UF
High efficiency condensing gas boiler in plant room
MHRV with water/air post heater unit run off HW tank, approx 2kw ( raises air inlet temp to about 20C when cold)
Zoned low temp underfloor down stairs
No heating upstairs
Heat dump on tank to outside for summer overheating

ps - have posted similar question over on Cons & Planning

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Well George, nice to see their is still someone other there with plenty of bucks, willing to look into different options.

My take on Passive House is a house that can sustain a decent living temperature without additional KW in energy provided by fuel. Most of the heat is regeneration / recycled from light builds to showers and everything in between, additional KW required for hot water by use of solar or geo. When you throw a condensate gas boiler in the mix you could be ruled out of having a passive house, if your thinking about gas boiler as a possible back up during system down time then you could be kept in the passive bracket. Saying all that I could be wrong, never really became involved in truly passive houses.

I've installed pretty much anything and everything for heating and hot water thats avail in some form or another from Oil, Gas, Geo, Airo, Argon, Solar and I've fitted all kinds of combination of those.

You mention a large ltr HW cylinder for stored hot water along with providing heat to UF? This is not something I'm used to seeing. It's possible to install a double contained type cylinder, outside cylinder is used to store heating water, called a jacket. Inside cylinder for stored hot water. Water circulates around entire jacket heating domestic water. For the same jacket to heat domestic water along with UF the jacket ltr capacity would have to be fairly large, I cant see any decent recovery of jacket without the use of an additional plate heat exchanger (gas boiler) when jacket is required to heat both domestic water along with UF.

You could be getting your wires crossed or maybe their is something avail I haven't seen yet. I more used to a buffer tank type installation taking up additional KW to serve UF , this tank is separate from hot water.

I've installed a few ventilation recovery units both stand alone and combined with Geo / Air. From my own experience the ones I've fitted seemed to cost a great deal but the cost far outweighed the benefit. I've worked in houses with only ventilation as heating, these systems are so finely tuned any fluctuation of air pressure within house can upset unit causing unit to work of back up immersion, all homeowner had to do was leave front door open longer than 30 secs. Again your linking recovery unit to hot water cylinder maybe in the view of hot water in jacket acting in some way to transfer heat to air, might be pushing the boat on this one but then again its not impossible.

All UF is low temp, never really gets up to high temperatures anything from 15 to 20's tends to be more than enough.

The heat dump for summer overheating might need to be included more in the mix and your being fairly optimistic that you'll actually have heat to dump even in height of summer. All depends on type solar collector, location of house, location / angle of panel etc so its hit and miss, no real way to tell until actually fitted. From what I know its a gamble, when people tend to rely on solar and push system from solar, m2 has to be worked out to provide enough KW's during worst possible weather condition, this leads to large solar collectors, then their is a risk of overheat blow outs, its a fine balance, I find most leave solar for hot water only as solar is unpredictable.

If your going down this route you have to take time and do homework, don't take anyone's word as gospel not even mine. I've fitted some of the top spec systems in some fairly high profile jobs, everything was designed / installed and commissioned to best of everyone's ability even still some of these systems had to rely on immersion / gas back ups which pushed ESB / gas bills up, at times some have wondered why go through all the expense and still high usage on back ups.

These eco, geo etc systems are a new concept, almost still on a trial / error period, I'm not even sure some of the latest manufacturers will last the duration, say in 5 to 10 years one of your systems breaks down, its possible their might not even be parts avail should they require replacing.

When you combine multiple systems you've got all kinds of programming to be aware of, its never a case of flicking a switch for heat and hot water everything has to be programmed. Multiple system means multiple maintenance, if one system fails their is sometimes a daisy chain effect. The amount of service options you have is limited to the amount of service people with enough experience in system you have installed, you could be waiting a while, well above the norm.

Best advice as always, never rush into it. If your building a house fit the basics you need to get yourself going and leave some provisions to allow use of the additional systems your interested in at a later date. If you happen to find the system you thought of might not work out from more research then no loss you haven't really committed to install. If things do happen to work out then no problem, provisions are their to complete works.

BigGeorge

Great comments - thank you.

A PH still has a heating requirement, just that is becomes very low, in the region cost wise of 300-400yoyo for DHW & heating per annum. This make it really hard to justify expensive heating equipment as the returns just are not there. Have run the house through the PHPP software and it passes with both a wood pellet boiler & the gas boiler.

As regards the MHRV unit, this is basically a requirement of getting the house certified so is necessary, the add on I'm investigating is putting a small amount of heat into the inlet air supply as I'm heard that the air can feel a bit cool especially as it would be about 16C during the winter - Scanhome & others do this with a elec element, so the principle is similar

On solar, I'm just looking to maximise the solar component and overcome any potential ( as an optimist...ya need to be sometime) summer overloading of the system

On the UF heating, I've just decided that I want background heating available when I want it, there may be some overkill I accept it, but I'm putting in the system to run over a long time period & need to be quite sure that it will perform through thick & thin - bit OTT though I accept that

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No bother, having such low annual usage of Gas / ESB (immersion) means they are only used as a last resort, almost like back up as mentioned before. Sounds like solar is going to be main heat source for both hot water and underfloor, its possible but requires a lot of thought, planning and so on.

MHRV type systems will have a diffuser plate attached to outlets, can act as a balancing tool also. Any of the ventilation units I've fitted I never noticed any excessive amounts of cold air while traveling below. No real pressure behind the air so going to the extra expense of partial heating might not be required at all. Most of the systems I fitted the extraction side (kitchens, living rooms with fires, bathrooms etc) heated fresh air side which takes the chill out of fresh air.

UF heating tends to run over long periods, it takes time to build up heat in floor to allow heat to dissipate into room and like wise when UF is turned off it takes some time before floor cools. Control of underfloor is by room thermostat, outside temp is a factor of room stat readings. Both room stat and outside temp readings control UF heating so correct operation depends on those two over an manual UF on / off switch. Adding some kind of weather compensating kit to control UF tends to be best option.

I'd look into almost over sizing UF heating by having installing more mtr of UF pipe. I'm not 100% sure of this, could be possible to heat house to required temp while UF working off lower than avg design temperature. Say standard UF sized to suit house working off minimum flow temp 18d, it might be possible to lower the working temp and still have house heating well by over sizing if you get me. Might be worth looking into.

Red Alert

How about something like this?

http://www.brinkclimatesystems.nl/passive-house-appliance/11745

It's by a dutch crowd. I came across them when I was investigating conventional warm-air heating.