Heat recovery and distribution at optimum temperatures

Heat-recovery-and-distribution-at-optimal-temperatures"Just do it" and save 50 %

When commercial cooling, heating demand and conventionally installed systems coincide, it is usually a case of paying attention. Under certain circumstances, there is considerable potential for saving primary energy. This is what happened at the SPAR store in Reichraming near Steyr. The reward: the award of the 'Energy Globe Award Upper Austria' End of last year.

You can make a 'doctoral thesis' out of any plant conversion. Often, however, a project is already off the table before the feasibility of the project has been diagnosed. Or else you start and do it. Because many years of experience, correct estimates and common sense are often the best advisors.

Fig. 1: SPAR market Reichraming

There is more to come

"In our case it was a defective circulating pump that tipped the scales," recalls senior Harald Landerl. For 37 years, his wife Maria has been running the only food market in Reichraming, Upper Austria. They have both lived there for just as long, as does son Harald and his family today. "Our well-known heating engineer Raimund Aschauer came by and took the opportunity to look at everything. His conclusion: "Harald, you can get something out of your system.

At first, Harald Landerl hesitated. Because saving always means investing first. This happened on a grand scale 10 years ago. At that time, the size of the store almost doubled to the current area of 416 m². The 55 kW pellet boiler and a new 45 kW refrigeration system were installed. Since then, a small part of the condenser waste heat from the refrigeration system has temporarily heated the small pool on the terrace. Most of the heat energy, however, went uselessly into the environment, as is the case with many commercial refrigeration systems. There was actually something to be gained here.

Fig. 2: Maria and Harald Landerl think the new heating concept in their SPAR store is just great.

Aschauer noticed another 'weak point'. Since the conversion 9 years ago, the son's house, which is located higher up, has been connected to the central heating system for the shop and his parents' house via a pipe about 20 metres long. This is a decoupled heating circuit, because due to the distance and above all the height difference of 22 metres, a heat exchanger had to be connected in between. A sensible idea, to be sure. However, since then, switching back and forth between the two heating circuits had to be done manually. This was not very convenient and often meant unnecessarily high operating hours for the pellet heating system. A buffer storage tank was not available. There is certainly room for optimisation here as well.

And then there was the heat distribution in the shop and the living areas via radiators, underfloor heating and ceiling radiators. Since the entire hydraulic network was connected to only one central heating system, the desired flow temperatures were achieved by adding cold water and distributing it with circulating pumps. This is still done today in countless installations. Effective, but nevertheless practised energy destruction.

50 per cent are possible

Fig. 4: Heat supplier pellet boiler

Fig. 3: Buffer tank with heat exchanger

Fig. 5: Refrigeration system

With these findings, Raimund Aschauer then sat down with his partner Albert Koppenberger. After an initial rough assessment, they were able to tell Harald Landerl some good news: "If we couple in the waste heat from the refrigeration system, install a buffer tank, convert the hydraulic system to rendeMIX mixers from Baunach and equip the entire heating system with a modern control system, you can roughly halve the annual pellet consumption". That was a word! Since, according to initial calculations, the expected amortisation of the conversion would be around seven years, entrepreneur Landerl did not think twice and placed the order. Because the attributes 'environmental protection' and 'resource conservation' are written in capital letters by the trained toolmaker and helped in the decision.

Fig. 6: Holger Müller explains the functions of the rendeMIX in apartment house 1 (an identical second 2×4 mixer now hangs in the junior's apartment house).

Two doers at work

Aschauer and Koppenberger (A&K) now worked out a sophisticated system, hydraulic and control scheme. The subsequent discussion with Hauser was positive and led to the result that the supplier of refrigerated cabinets and refrigeration technology added a heat transfer module to the new buffer tank customised by A&K. Since then, the condensation waste heat generated is decoupled from the refrigeration circuit via this module and fed directly into the buffer at a temperature level between 45 and 50°C. Since a supermarket refrigeration system has to be in operation all year round, there are hardly any phases without heat dissipation. If, nevertheless, the waste heat from the refrigeration system is not sufficient to generate the required storage temperatures, only then does the pellet boiler reheat the double-layer buffer storage tank with a capacity of 2200 litres. And if no waste heat is required, the installed axial condenser of the refrigeration system is still available for discharge to the outside air.

The new hydraulic conductors

With this measure alone, significant savings could already be expected. The second major potential then lay in the distribution and buffering of heat. Raimund Aschauer remembered a seminar held by HG Baunach GmbH. At that time, Holger Müller presented the rendeMIX in Wels. A multi-way mixer that was a perfect fit. "When it comes to efficient coupling of radiators and underfloor heating, our patented system delivers the best results," Müller said.

Fig. 7: Successful project partners (from left): Holger Müller, Harald Landerl jun., Albert Koppenberger, Raimund Aschauer.

"The radiator return becomes the flow for the pipe coils in the floor. An intelligent control system in the 2×4 mixer ensures that the mixing ratios and temperatures are precisely maintained. "Another plus: the suction circulating pump for the mixing circuit is already integrated in the assembly. Hydraulic points, sensors or an additional controller module are also unnecessary. "You could say that the rendeMIX becomes the conductor of the entire hydraulic system," Müller summarises the benefits strikingly.

Conversion in only four weeks

In August 2014, the work began. And within just four weeks, the work was done. The double-layer buffer storage tank, insulated with sheep's wool, stood in the boiler room, which is located in an outbuilding between the two residential buildings (see graphic).

Fig. 8: Diagram of the simplified schematic of the entire heat cycle, shown on the basis of the real conditions on site.

The hot gas side of the integrated system was connected to the heat exchanger module by Hauser. Because the refrigerant has to be evacuated and refilled for this, a refrigeration specialist is needed. Then, in the basements of each of the two residential buildings, a rendeMIX DN25 2×4 RH35 and connected on the supply/return side to the heat supply and to the radiator and underfloor heating circuits. At the same time, three circulation pumps became superfluous. Electrical specialist Albert Koppenberger came up with an ingenious concept for the control system. With the freely programmable UVR controllers from the manufacturer Technische Alternative, Amaliendorf, the entire heating system is now intelligently networked.

Fig. 9: New UVR controller in the boiler room

This has made manual interventions superfluous. Instead, the thermal energy is efficiently extracted and buffered on the generator side according to a logical function and only ever shifted to where it is needed. Today, the flow temperatures for all heating circuits are lowered to such an extent that no loss of comfort occurs, but also only as much heat energy has to be added as is needed. This is ensured by the two rendeMIX mixers. The weather-compensated control ensures that no room cools down too much at night. For this reason, the water in the heating circuits is permanently circulated at a temperature level between 38 and 40 °C. If one of the two boilers in the residential buildings requires higher temperatures between 6 a.m. and 10 p.m., the flow is briefly increased to 55 °C and then lowered again once the storage tank has been loaded. Only the boiler in the department stores' is heated electrically in order to maintain the temperatures required by hygiene regulations.

Fig. 10: The beautiful confirmation of a visionary idea. Albert Koppenberger with the certificate of the Energy Globe Award Upper Austria.

Expected savings in sight

The fact that Aschauer and Koppenberger did not promise too much was already foreseeable at the time of the plant inspection at the end of February 2015. "Since the pellet boiler was installed 9 years ago, I have always ordered fuel twice a year," recalls Harald Landerl. "In September, 13 tonnes and in February another 10 tonnes. And now look how much is still there after the first delivery since September 2014." A glance at the storage tank suggests that it is still just under half full. "I won't have to reorder until the end of the 2014/15 heating season. And there will probably even be some left over, so effectively between 10 and 12t of pellets will be saved." This means that the reality is very close to the estimate of 50% made at the beginning of the project. Almost a precision landing, then.

A positive conclusion

To summarise: The waste heat level of a refrigeration system can be used sensibly for heating and hot water preparation if there is a simultaneous demand for heat. Intelligent control is the key to demand-oriented heat provision. And the rendeMix mixer prevents heat from being wasted in heating circuits with different flow temperatures. The combination of these measures has brought the Landerl SPAR store around 50 per cent energy and cost savings, as well as the two system builders Aschauer and Koppenberger the Energy Globe Award Upper Austria 2014 in the category 'Fire' as a special distinction. Once again, congratulations to all those involved for a real showcase project - which was simply done.


The rendeMIX can do more

In addition to the coupling of a high-temperature and a low-temperature circuit, as in the example of SPAR-Markt Landerl, the four-way mixer rendeMIX can also be connected directly to a stratified buffer tank. It then enables two-zone charging and discharging. The advantage is that hot, cold and mixed water (by using the return flow) only flow in and out of their respective zones. A safety shield is thus built up in the middle of the buffer. The stratification in the storage tank is thus maintained. In addition to this effective loading, the rendeMIX also efficiently discharges a storage tank. This can be used, for example, to economically extend the running time of solar systems or small CHP units. And because the return flow of the radiators becomes the flow of the underfloor heating, the water flows back colder to an oil or gas condensing boiler. This produces more condensate and more condensation heat from the flue gas gets into the heating water. This effectively saves primary energy.


Achim Frommann

PR Workshop NutzWort

Sasbach (Germany)

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