Mikey_1980

6 Months with the Ecocent

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Hi, I hope everyone is well, I just thought I would provide an update on how things are going with our Ecocent after 6 months use, and now that I have some data for the past few months where we have had below 0 temperatures.  For those that can remember there was a debate over potential big temperature drops when the ecocent came on over on ebuild, here is the link http://www.ebuild.co.uk/topic/18060-i-have-bought-an-ecocent-and-everything-else-esp-do/

 

Well I am pleased to say that we haven't experienced anything like that, I am monitoring the temperature via the 12 Heatmiser Themostats we have installed around the house and there is nothing more than a degree of temperature varitaition during a 24 hour period, from any of the thermostats with house set around 22 degrees, we also are using the Earthsave Varimax ASHP to heat our 280m2 ground floor slab. I am waiting on our Electricity usage to come through so can't give the numerical figures yet but so far we are very happy, and only once have we run out of DHW from the 300 litre tank but we did have around 9 adults all trying to shower in the space of an hour.

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Thanks for the update, let us know when you have the electricity usage (what's stopping you reading the meter?)

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Yes, useful to know, as it means that the UFH can pump enough extra heat in to the house to make up for the heat removed by the Ecocent, something that bothered me in terms of response times.

 

Out of interest, what's the UFH flow temperature?  We keep ours at around 24 to 25 deg C maximum, as any higher tends to cause a fairly large (greater than 1 deg C) temperature overshoot after the thermostat's satisfied.

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Just like @Mikey_1980 we are running an Ecocent. It is in our rental cottage which we now use whilst new house is built. Picking up on @JSHarris point of flow temperature i have been reducing the temperature gradually from 40 to 35 as we were having the temperature overshoots mentioned. Its been at 35 for 4 weeks now and we still find that it is overshooting late evening so needs to drop some more. There has been no noticeable change in the time the Ecocent comes on. Our Ecocent is set to come on when there is a temp drop in the water so it extracts the heat from showers etc (our wet room can go from 21 to 26 after a shower). I don't have the monitoring systems in place to measure anything accurately its more about comfort. Last night we had -5.5 deg and have had -9 this year and both systems have coped well and have not been working flat out as i had expected.

I am currently looking at how to simplify the control down stairs so it acts as one large circuit to even out the heat rather than having 4 zones and trying to match the on off and temps 

 

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I'd not expect the slightest problem with an Ecocent drawing heat from a house with that much heat input; your UFH is pumping many times more heat per unit area into the floor than our is, so the additional heating requirement imposed when the Ecocent turns on is pretty small in comparison with the other heat losses. 

 

That's the sort of application where exhaust air heat pumps, or room air draw heat pumps, work fairly well for DHW.  Where they don't work well is where the house heating requirement is so low that the additional heat loss when the Ecocent turns on cannot be quickly accommodated by the heating system ramping up to push extra heat into the house.

 

The Ecocent doesn't "make heat", it only sucks low grade heat from the house, that's been heated by some other means, upgrades it and heats hot water with it.  That means it always has to draw around three quarters of the heat it puts into the hot water from the inside of the house, and that heat has to come from somewhere.

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Someone should create a spreadsheet to work out the sweet spot... is it doable with given space heating loss and DHW requirement?

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So answers to questions are

Our UFH is running at 28 degrees.

I haven't been monitoring the electricity usage closely and we have been doing alot of work still so the next 3 months will give the best indicator for usage, we are also only just moving from business rates to residential as it is something I never got round to doing.

The install cost was less than £20k, this was for the Ecocent, MVHR and ASHP, all pipework/controls/installation everything taking the bare UFH pipes to a full functioning Heating/MVHR/DHW system and our plumber ran all the Hot and Cold pipes back for the Ecocent to be connected to

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52 minutes ago, gravelld said:

Someone should create a spreadsheet to work out the sweet spot... is it doable with given space heating loss and DHW requirement?

 

 

Not sure there is a sweet spot, really.  It largely comes down to the response time of the house heating system in being able to put back the heat sucked out by the Ecocent.

 

If you're using a heat pump as the heat source for the house, then what you achieve with the Ecocent is a two stage heat pump, with a stack of losses, in effect, in the intermediate stage (the house heating requirement).  To work OK, then the house heating system has to be able to respond to any heat loss quickly enough to not impact on the room temperature too much (there has to be some impact on room temperature as usually room temperature controls the "first stage" of this two stage system).

 

You need to design the total system (heating and hot water) so that the heating system can deliver the extra  power needed to provide the heat input to the Ecocent (a couple of kW or so) when it turns on.  The idea above, of timing it to come on when there is an excess of room heat from the shower having been run is a good one, although it would naturally tend to come on then anyway because of the hot water use.

 

To give a specific illustration, our house needs a few hundred watts of heat at most to stay at around 20 to 21 deg C.  If we had an Ecocent we'd have to find a way to put three to four times more heat into the house whenever the Ecocent was running, and do it quickly.  I could turn the UFH flow temp up; turning it to 28 deg C would definitely do the job OK in terms of additional heat input, but then I'd hit the snag I've already found; at 28 deg C flow our room temperature overshoots  a fair bit when the heating switches off because the thermostat is satisfied.  I dare not turn up our flow temperature above 25 deg C, and ideally I'd like to keep it around 24 deg C if I could, because of the overshoot problem.

 

The problem is that the slab response time is pretty long, so when you start pumping heat into the pipes it takes a fair time for it to reach the surface and start heating the house.  If the heating turns off, because the house is warm enough, heat continues to be released by the slab for several hours, as the warmer core of the slab slowly transfers heat to the surface and thence to the rooms.  The less warm the core of the slab gets from the UFH, the smaller the overshoot problem.

Edited by JSHarris
typos

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I can totally understand it won't work for your house Jeremy, I meant that I wondered whether there's a sweet spot with less performant dwellings.

 

The sweet spot may also relate not just to the technical questions of balancing the heat loss and DHW demand, but also the woolier demands of an overall building project. For example, might this be a good fit for a refurbishment project with reasonable aims at low-ish energy (let's say AECB Silver), if it also ticks the ventilation box, without having ducting which might otherwise by overly disruptive.

 

I don't know the answers to these questions and my examples are purely speculative.

Edited by gravelld

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25 minutes ago, gravelld said:

I can totally understand it won't work for your house Jeremy, I meant that I wondered whether there's a sweet spot with less performant dwellings.

 

The sweet spot may also relate not just to the technical questions of balancing the heat loss and DHW demand, but also the woolier demands of an overall building project. For example, might this be a good fit for a refurbishment project with reasonable aims at low-ish energy (let's say AECB Silver), if it also ticks the ventilation box, without having ducting which might otherwise by overly disruptive.

 

I don't know the answers to these questions and my examples are purely speculative.

On it's own, it won't meet the ventilation requirements, for two reasons.  Firstly, it only sucks air from the house when it needs to heat water, and that may or may not coincide with when you need ventilation.  As an example, you may be cooking, so need extra ventilation, but the hot water tank may already be hot, so the ecocent won't run.

 

ESP can combine it with a simple MVHR (like a few other systems that are available), which is sort of OK.  When the Ecocent isn't running the MVHR works as normal, with the flows balanced and the flow rates set to those needed to meet the ventilation requirement.  However, when the Ecocent runs the flow rates massively increase, and the MVHR goes way out of balance.  The consequence of this is that heat recovery to the room air during these periods is very low, far lower than when the system is running normally.  That's just a function of the way heat exchangers work, and can't be avoided. 

 

However, the impact this has may not be that massive, as you don't need to heat water all the time, only for a few hours a day, so most of the time the MVHR works normally, with normal heat recovery rates.  The fact that the MVHR loses efficiency a lot for a few hours is still better than no MVHR at all, by a long way.

 

To be fair, we should also include the other combined systems, like the Paul and the Genvex that are also MVHR units with an added exhaust air heat pump to heat hot water, as they all operate in the same way and have the same pros and cons.

 

They are absolutely ideal if you have a house that has somewhere that's consistently too warm.  As an example, we stayed in a well-insulated log cabin, with a wood burning stove.  There was a mezzanine storage area in what could have been a small loft, and up there it was always like an oven.  Drawing air from there to run an exhaust air heat pump for hot water would have been ideal, as it would have made use of what was probably a fair bit of otherwise waste heat.

 

Someone on another forum has an Ecocent and (IIRC) they feed it with air that comes indirectly from a workshop (heated with a wood burner in winter) that's connected to  a glazed sun room (that tends to get warm in summer) alongside the house and that feeds the air to the Ecocent.  This results in virtually no impact on the house temperature, by making use of otherwise wasted heat to deliver hot water.  I think the only issues I've heard of with this set up was the stainless tank in the Ecocent corroding and failing.  IIRC there is a protective anode that needs to be regularly inspected and replaced when corroded, just like many stainless tanks.

Edited by JSHarris

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Put another way, is it that fast recovery is the issue? I think I naively thought that leaving it to run through the day would slowly build up enough energy in the tank, but then as I think ST's calcs showed in the other thread, there just wouldn't be enough air or high enough exhaust temperature to provide enough energy. But this definitely wouldn't work if the tank was depleted and needed immediate energy.

 

If the ventilation rate was increased as you say and the energy was exchanged back into the water, it's not being wasted is it, other than the losses of the heat exchanger?

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49 minutes ago, gravelld said:

Put another way, is it that fast recovery is the issue? I think I naively thought that leaving it to run through the day would slowly build up enough energy in the tank, but then as I think ST's calcs showed in the other thread, there just wouldn't be enough air or high enough exhaust temperature to provide enough energy. But this definitely wouldn't work if the tank was depleted and needed immediate energy.

 

If the ventilation rate was increased as you say and the energy was exchanged back into the water, it's not being wasted is it, other than the losses of the heat exchanger?

 

Yes, it is the "on/off" nature of the heat pump in these things that is a part of the problem (and it's not just the Ecocent, the Genvex and Paul units similarly have a non-modulating heat pump). 

 

The basic units are extremely common in China, where there are literally hundreds of companies making them, and they are all very similar in design.  The Ecocent was originally just a badged Chinese unit, but when I spoke to the guys from ESP (who are very helpful and technically pretty switched on) they told me that it was all made in the UK now.  I have to say I have a few doubts about that, as there are physically absolutely identical units still on sale on Alibaba etc, and ESP has a long history of importing Chinese equipment, getting it approved to EU regs, and then re-badging it.  However, where it's made doesn't matter, it's the "all or nothing" nature of the heat pump that's key.

 

The reason for this is two fold.  Firstly, these units are designed to replenish the hot water tank as quickly as possible after use, so there is always hot water available.  Secondly it is a heck of a lot cheaper to build a non-inverter controlled heat pump, that only runs at a single speed.

 

Depending on the pattern of hot water usage, an inverter-controlled version might well be a good option.  For example, our major hot water demand is first thing in the morning for showers, then there is virtually no demand at all through the day, with a small demand in the early evening for washing dishes (just the stuff that doesn't go in the dishwasher) and very rarely an evening bath.  A unit that could very slowly recharge during the day, drawing only as much heat from the exhaust of the MVHR as allowed by normal MVHR flow rates, would be fine for us, as our available recharge periods are always going to be 8 to 10 hours or more.

 

The alternative, for those that need the maximum recharge rate, is to have a heating system that is responsive enough to increase its heat output in time with the additional demand that the water heating heat pump needs (I'm trying to be non-brand specific here, as this applies to all exhaust air to water heat pumps).  There is loads of available energy in the MVHR exhaust, but to extract it at normal flow rates needs a very small capacity (or variable capacity) heat pump.  The alternative is to increase the ventilation rate to get enough mass flow of air through a larger air to water heat pump.

 

However, if the ventilation rate is increased, then the MVHR heat exchanger efficiency will drop, a lot, as heat exchange efficiency is very closely tied to flow rate.  This means that incoming cool air won't get warmed anywhere near as much and so will be a lot cooler, and tend to cool the house down more than it would when the ventilation heat recovery system is working at normal flow rates.  There is no good way around this.  One sort of fix (and one that I think some systems use) is to draw outside air in and mix it with the MVHR exhaust, so that the MVHR doesn't end up delivering cold air.  The downside with this method is that although the MVHR efficiency then ends up OK, the efficient of the air to water heat pump drops, as its inlet temperature is reduced by mixing outside air with the MVHR exhaust (which is always a couple of degrees warmer than the outside air).  I've seen another fix where there was a valve fitted to the MVHR external inlet to just throttle the incoming fresh air, and allow air leakage to deal with the resulting flow imbalance.  Clearly any incoming leakage air will be at outside air temperature, so will cool the house, but because it would probably be distributed over a lot of small, tiny, leakage points the effect may not be as obvious.

 

For me, a small, inverter controlled, variable output, exhaust air to water heat pump could work well, as I could easily accept long recharge periods.  I've looked around, and so far I've not found a modulating unit like this.  My guess is that this is just down to demand.  There is a massive demand in China for these things, do a search on Alibaba and you'll probably be as surprised as I was at how many manufacturers of them there are.  Nothing in the Far Eastern market is driving manufacturers to invest in inverter controlled units, and I have to say that it's really only people with low energy homes, plus a pattern of hot water usage that allows for fairly long recharge times, that would really benefit from such a unit.

Edited by JSHarris
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15 hours ago, JSHarris said:

...

 

Depending on the pattern of hot water usage, an inverter-controlled version might well be a good option.  For example, our major hot water demand is first thing in the morning for showers, then there is virtually no demand at all through the day, with a small demand in the early evening for washing dishes (just the stuff that doesn't go in the dishwasher) and very rarely an evening bath.  A unit that could very slowly recharge during the day, drawing only as much heat from the exhaust of the MVHR as allowed by normal MVHR flow rates, would be fine for us, as our available recharge periods are always going to be 8 to 10 hours or more.

 

The alternative, for those that need the maximum recharge rate, is to have a heating system that is responsive enough to increase its heat output in time with the additional demand that the water heating heat pump needs (I'm trying to be non-brand specific here, as this applies to all exhaust air to water heat pumps).  There is loads of available energy in the MVHR exhaust, but to extract it at normal flow rates needs a very small capacity (or variable capacity) heat pump.  The alternative is to increase the ventilation rate to get enough mass flow of air through a larger air to water heat pump.

 

...

 

For me, a small, inverter controlled, variable output, exhaust air to water heat pump could work well, as I could easily accept long recharge periods.  I've looked around, and so far I've not found a modulating unit like this.  My guess is that this is just down to demand.  There is a massive demand in China for these things, do a search on Alibaba and you'll probably be as surprised as I was at how many manufacturers of them there are.  Nothing in the Far Eastern market is driving manufacturers to invest in inverter controlled units, and I have to say that it's really only people with low energy homes, plus a pattern of hot water usage that allows for fairly long recharge times, that would really benefit from such a unit.

 

Thanks Jeremy.

 

Another approach may be to solve the problem at a different point. Is the system too closed to not allow other heat inputs, or different ways of drawing hot water?

 

For example, PV or solar thermal could top up the temperature, or even a system boiler might be a good idea if you can have a modern gas boiler installed.

 

Also, you could make do with lower temperature in the tank if you had inline modulating heaters like yours, right?

 

However, that still assumes you can just have a exhaust air heat pump which doesn't go into overdrive, and will just through the day trickle energy in at the ventilation rate.

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I'm pretty sure there's an immersion heater element in some of these systems, to allow for PV top up, and a couple also allow for solar thermal input too, via a high efficiency coil, and that could be used with other low grade heat sources too.

 

The bottom line is that really all these things are is a fixed speed air to water heat pump fitted to a water tank.  They don't care where the inlet air comes from or the outlet air goes to.  They are technically no different at all from a conventional (but rather small) monoblock ASHP, and work in exactly the same way.  They do select a refrigerant that works better at higher air input temperatures, because the principle design point for these things (direct from an ESP bloke I was talking to, ages ago) is an air input temperature of 25 deg C and a hot water temperature of 50 deg C, where they will deliver a COP of better than 4.

 

Like any ASHP, increase the temperature differential between inlet air and output water and the COP goes down, and also you start hitting the double whammy of getting  defrost cycling.  They get the high heat pump efficiency by drawing in warm air from the house, which maintains the low temperature differential needed.

 

The key thing is to work well the house has to have a heating system that can provide the heat needed to feed the air inlet of the unit.  There are several ways of doing this, but the major stumbling block is that when running these things use a LOT of warm air, far more than a normal sized MVHR exhausts.   That has to come from somewhere.

 

When you do the numbers, an exhaust air fed heat pump is barely better than an outside air fed heat pump in cold weather.in terms of efficiency, because, within reason, intake air temperature has only a small impact on the heat energy available for the heat pump to extract.  For example, air at 2 deg C contains about 1% more heat energy than air at -1 deg C, or air at 20 deg C has about 7% more heat energy in it that air at 0 deg C. 

 

Right now the air coming out of our MVHR exhaust is only 3 deg warmer than the outside air temperature, and frankly that makes the difference in COP between an outside air fed heat pump and an exhaust air fed one negligible, and not worth the additional expenditure, in my view.  I get a far, far bigger difference in COP from having an inverter controlled, variable output, ASHP, as that can modulate down and avoid the defrost penalty, something a fixed speed unit can't do.  The variable speed advantage in efficiency terms is probably well over 10%, and that exceed any difference from feeding the thing with warm air.  The downside is that all heat pumps only have a limited temperature differential over which they work very efficiently, and that's typically around 30 to 40 deg C.  Any more than this and efficiency falls off, rather non-linearly I've found..

 

These integral water tank and heat pump units were designed for homes where there was plenty of heat available inside the house, and they work very well under those conditions.  As other companies have found, trying to make them work well in a house that doesn't have a good heating system that is separate from the unit is challenging.  Paul, for example, got caught out (or, more accurately, a UK agent selling Paul stuff who got his/her sums badly wrong) got their fingers burned when they installed a load of their very similar (functionally) exhaust air heat pumps in social housing.  They found that the electricity usage was excessively high, because poor system design meant that the air temperature going into the unit was too cool and the unit was compensating by running its internal immersion heater a lot of the time to make up for this (the Paul and Genvex systems have an internal immersion that's automatically controlled by the built in controller).

 

 

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Hi all, 

 

I would like mention the Ecocent is now listed on SAP as a (MEV) hot water heat recovery system.

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