【 Weak current College 】 household heat metering design

1, introduction

In March 2001, the countries on the heating, ventilation and air conditioning design code GBJ19-87 heating parts of a partial amendment to set up household heat metering and room temperature control device as a mandatory requirement. Beijing in December of 2000, the Beijing Municipal standards: the new central heating household metering technical specification for the design, the design of heating-based heat metering has made a series of specific provisions. At the national and local mandatory standards, new residential hot water central heating system generally had a design-based heat metering. The authors are working on a design quality pumping (Tribunal) enquiries, contact with some household heat heating engineering design, overall, basically in line with the relevant norms, standards, procedures, but also found some debatable issue. The identified problems and personal ideas are summarized as follows:

2, the relevant standards, regulations, norms of recalling

Since 1996, the countries on the new central heating residential design based heat metering, promulgated the regulations, specifications, terms and expressions is gradually clear, more and more strict.

1996, 7 1 January of the civil construction energy conservation design standards (existing building) section 5.2.2 JGJ26-95 stipulates: "the indoor heating system design, designers should consider household metering and the possibility of controlling the temperature of the room."

1 June 1999 onwards, the residential design code GB50096-1999 section 6.2.3 stipulates: "centralized heating system design should be able to implement individual room temperature control and for the implementation of the household heat metering reservation conditions".

1 October 2000 States that the promulgation of civil construction energy conservation management regulations "(Ministry of construction make 76) article 5 stipulates that:" new residential buildings ofcentralized heating system should use the double-pipe system, the implementation of the temperature adjustment and household heat metering device ".

1 December 2000 introduced in Beijing, Beijing, standard: the new central heating residential design technology based heat metering code DBJ01-605-2000, on Beijing's heat metering design for specific norms. This is the earlier of the household heat metering design of local regulations. For other heating area household heat metering design provides reference.

1 April 2001 States that the purpose of heating, ventilation and air conditioning design code GBJ19-87 heating section 2001 local modification for 3.9.1 stipulates: "the new residential hot water central heating system should be set based heat metering and room temperature control device" and set this provision as mandatory provisions, the requirements of the design must be strictly enforced.

1 September 2001 the Beijing municipal building energy management regulations (Beijing Municipal People's Government order No. 80) article 8: "the new building project must select advanced reasonable heating way, using efficient pipe insulation and thermal regulation and metering technology and energy-saving materials, equipment, apparatus.

In the design of new residential heating, indoor systems such as still uses the traditional vertical single-pipe-line system or vertical single-, double-pipe-line system, it is difficult to meet these specifications, procedures required to traditional heating systems in the form of radical change, "the use of common legislation of individual independent system forms", "according to the household design heat meter heat measurement method for design" so that a a table.

3, indoor temperature

Should be distinguished from non-household heat metering of ordinary residence does not take into account household heat metering of ordinary housing, indoor temperature should be according to the literature section3 in 6.2.2, indoor temperature minimum calculation: bedroom, living room (Hall) and the bathroom 18 ° c, 15 ° c in the kitchen, bath and have centralized hot water supply system of bathroom design should be 25 ℃.

Using ordinary household heat metering, reference literature House 5 provides value, the calculation of indoor heating the room temperature should be in the literature on the basis of 3 and a corresponding increase in the 2 ° c, i.e., bedroom, living room (Hall) and the bathroom 18 + 2 = 20 ° c, kitchen 15 + 2 = 17 degrees centigrade. The original press 20 ℃ or 22 ° c calculation of senior housing, the use of household heat metering, the bedroom, living room (Hall) and the bathroom should be 20 + 2 = 22 + 22 ° c or 2 = 24 ° c, the occupants have a certain level of thermal comfort of choice.

But some of the new central heating residential use of household heat metering system, the indoor temperature is still provided by literature 3 bedroom, living room (Hall) 18 ° c, is inappropriate, the occupants little thermal comfort choice, as well as design, whatever the nature of room, indoor temperature will be according to 18 ° c or 20 ¡æ use is inappropriate, according to the different rooms of different functional requirements, the selection of different temperatures, such as the kitchen should be 15 ℃ ~ 17 ° c, and not according to 18 ° c or 20 ° c, with bath, and a centralized hot water supply system in the bathroom should be 25 ~ 27 ℃, and not according to 18 ° c or 20 ℃.

Set up household heat metering, when using the low-temperature radiant floor heating system, heating heat load calculation should be indoor temperature 2 ° c; because the radiant floor heating is a radiant heat and air temperature in the dual role of room heating, forming a more reasonable indoor temperature distribution and heat radiation effect, relative to conventional convection heating method can have 2 ~ 3 ° c thermal comfort of equivalent effect, for security reasons, the document 6 indoor heating calculation temperature 2 degrees centigrade. As the Beijing area, outdoor heating calculation temperature of-9 ° c, on household heat metering of ordinary housing, bedroom, living room (Hall) indoor temperature 20 ° c to 29 ° c temperature difference calculation, floor heating, press room, 2 ° c value should be calculated temperature 27 degrees centigrade; its senior residence, bedroom, living room (Hall) 22 ° c, the temperature 31 ° c, calculated with floor heating, press2 ° c room temperature, lower values should be calculated temperature 29 degrees centigrade. For floor hot water heating system, the indoor temperature reduction of 2 ° c, i.e. 18 ~ 20 ¡æ heating load calculation, as the equivalent thermal comfort effect, the same can reach indoor 20 ~ 22 ° c of temperature effects.

4. heat transfer across

Not included in the total heating system heat load internal implementation of household heat metering and lab control temperature, there will be some room heating, partial room relatively big batch use or adjust the room temperature, which must take into account heat transfer between the impact load. But this problem can have two programmes: one room with adjacent due to variations in the form of heat, can be used to improve the indoor temperature, the main room and press the appropriate design standards increase the 2 ° c, heat transfer between the temperature of the load may 6-8 ° c, the second is necessary household interval appropriate wall and floor insulation, thermal insulation for maximum heat transfer coefficient, the author believes that you can reference literature 2 4.2.1 table 4.2.1 external wall (shape coefficient ≤ 0.3) heat transfer coefficient limits access.

The heat transfer between households should be considered, this is no problem, but it must be clear that the heat transfer between does not make the gross heat load increases, the heat transfer between load is only available as indoor heating equipment factors should not be statistics in heating systems within the total heat load. Literature 1 3.9.3 stipulates that "in determining the heat metering system for indoor heating equipment capacity, calculation of indoor plumbing, accrued in the adjacent caused by additional heat, but the additional calories should not have statistics on heating system within the total thermal load." Literature 5 3.0.6 also provides: "heat transfer across only as indoor heating equipment capacity and calculation of indoor plumbing, not included in outdoor heating dry pipe heat load and thermal load in total construction."

In the actual engineering design, HVAC designers did not note the heat transfer across and indoor heating equipment capacity and building total heat load of this mutual relationship, and the heat transfer between the building load also included in the total heat load, resulting in increased heating total heat load more wastage.

A-level cadres, residential buildings, a building area of 6295m2, design uses household heat heating system, heating load 558.3kW, unit area heating load index up 88.7W/m2; while some military housing, construction area of 9524m2, 419kW total heating load, thermal load per unit area heating indicators only 44W/m2. both the heat load per unit area indicators differ by more than doubled. The reason, besides the two building envelope insulation practices, heat load calculation parameters slightly, mainly of the heat transfer between the statistics in the heating system, the total heat load while the latter only the heat transfer between load as indoor heating equipment capacity and indoor plumbing, are not included in the total heat load, causing its heat load index per unit area has so much different.

5. household heat meter

It is located in indoor literature 1 3.9.5 stipulates: household heat metering hot water central heating system for the sharing of risers and home appliance yishe to pipe wells, pipelines, well advised to neighboring stairs or outdoor public space ". 5.3.3 document 5 stipulates: "share the standpipe yishe outdoors and lock valve and household heat meter combination set to lock seal tube or small room", "household hot table settings in the indoor, lock control valve and calorie display unit should be set outdoors". Here on household heat metering hot water central heating system with riser and home appliance set location and definite requirements, public standpipe and indoor entrance (including heat meter and locking control valve and so on), at least in outdoor yishe lock valve and calorie display unit should in outdoor settings. In this way, both to meet the needs for public function set of pipes, and also to prevent man-made damage, easy management, avoid at-home reading table.

Some new residential use of heating system-based heat metering, will share the risers and household hot table located in the North balcony, some of the new household metering design using low-temperature radiant floor heating, will share the risers and household and set water located in the Hall, household heat meter has to stay here, this is wrong, check the heat when the table is also home to read table, management inconvenience.

6, radiator

Thermostatic valve should be aware of its sensor selection and sets the radiator thermostat valve is household heat metering systems at room temperature regulation of important device, its sensor selection and sets whether the installation of heating with radiators on the hood. If the building is located on the heating cover, thermostatic valve sensor can be built-in, such as building set heating cover, thermostatic valve with external sensor should use. 3.3.12 in literature 1 stipulates: "the installation in decoration shroud of thermostatic valve must be in an external sensor". The sensor should be set correctly reflect the location of the room temperature.

Some new residential project based heat metering systems, each radiator water supply pipes are fitted with thermostatic valve, but does not specify a built-in or external sensor, architecture design description explicitly required each radiator are equipped with heating cover, so that construction installation may be wrong: If you ordered the construction, installation of a built-in sensor of the thermostatic valve, it will lose control of room temperature, as in the heating of the sensor inside the hood reflected heating cover within the local temperature, not the indoor temperature.

The author believes that the heat sink provided with thermostatic valve of the heat metering systems, to ensure that the effect of room temperature control, best no heating radiator cover, which will save money used to purchase and install energy-efficient and with decorative features of heatsink (currently many radiators have this feature, design choice is quite big). If the heatsink design selection is both energy-efficient, coordinated with the construction decoration, good decorative features, the user is perfectly acceptable. If a user is bent on loading heating cover, HVAC design file must be specified using an external sensor of the thermostatic valve.

7. heating and hot water piping buried

Flow rate should be consistent with the normative requirements document 1 3.8.18 stipulates: "the heating pipe laying there should be a slope, on hot tubs ... Gradient use 0.003, shall not be less than 0.002 ... ", this is a traditional heating system purposes. For household heat metering system, if available, return water pipeline downlead, you should implement this requirement. But if the pipes are laid in the cushion, mat thickness limited, pipeline also request press ≥ 0.002 slope laying is difficult. Therefore, this article also provides that: "as a result of conditions, water pipe (including the level of single-pipe-line systems radiator connection tube) can be laid without gradient, but in the flow rate must not be less than the 0.25m/s". Literature 5 pipes 6.4.4 bar also provides a "No grade laying, pipe flow velocity is not less than 0.25m/s". This provision is considered easy to exclude the air, when the water flow velocity reaches 0.25m/s can be put in the air bubble away so that it does not float. Practice has proved that the water heating system air is the most harmful factors, when there is air in the stock, often affects the normal circulation of hot water, causing some parts not hot, generate noise. HVAC design professionals to effectively exclude air must cause sufficient attention.

Some residential project based heat metering systems, the use of different leg of the level of single-hose system, located in 80 ~ 100mm thick mat of pipe laying for no slope, a household is divided into several heating loop, cause many pipe flow velocity in < 0.25m/s, can not meet the specification of the minimum velocity limits may cause localized product gas pipeline, affect the normal use of the system. It all depends on the systems collar, not too small, indoor system is much better to have an horizontal single pipe reverse return system, pipe diameter selection should not be too large, the average ratio of friction in the pipeline should be 60 ~ 120Pa have access, within the pipes to the hot water flow rate does not exceed the maximum permitted speed limit.

8, the hydraulic balance calculation

Should consider the vertical sharing risers of gravity head at the moment, new household heat metering system design, generally uses the new two-pipe system, namely the sharing of risers in the form of household independent heating system. This system is used in the calculation of the total of the standpipe of the hydraulic balance between parallel loops, accrual and vertical and horizontal sharing of standpipe gravity head to avoid vertical imbalance.

Literature section 7.2.4 in 5: "the parallel loop hydraulic balance between accrued and vertical sharing risers of gravity-head". Gravity-head values can be designed for the return water temperature conditions of gravity-head value 2/3. When the backwater temperature 95/70 ° c, its gravity head computed value △ P = 2/3 (977.81-961.92) h = 10.59h (kg/m2), such as layer high h = 2.8m, each tier computing gravity head value 29.65kg/m2 (mmH2O). When the backwater temperature 80/60 ° c, its gravity head computed value as △ P = 7.6h (kg/m2), such as layers to 2.8m, each tier computing gravity head value 21.28kg/m2 (mmH2O).

Some new residential heating design based heat metering, in calculating the sharing of standpipe hydraulic balance between parallel loops, did not consider this a gravity-head value, may bring the parallel loop (all households) hydraulic imbalance, vertical hydraulic imbalance occurs, resulting in uneven cooling, up and down.

9, public rooms in the residence, public space should separate settings for the heating system and heat metering device literature 1 3.9.1 stipulates:

"On the construction of public buildings and public spaces should set up a separate heating system and heat metering device". 5.4.1 documentation 5 also provides: "the House of public buildings and public space should be set independent heating system and heat metering device", residential buildings in the public and the public space is a residential building at the bottom of the shopping malls and other public places and basement office, equipment, inventory, and other public buildings.

The basement of a high-rise residential building for Office space, the heating system is equipped with six heating loop, the for each loop back to the water mains are separate from the building supply, backwater stem fittings, access (in the upper main risers are thus available, backwater stem fittings out access) without a separate set of heat metering device, it does not meet specifications. This system is not conducive to heat metering device independent setting, this system if heat metering unit, set of 6 sets, apparently irrational, not economic. A more reasonable and economic practices should be: from building supply and return water dry pipe separate way, then the rational organization of the Office building, ground floor heating system and on a site separate set a metering device.

10, design choice of plastic pipes

Should indicate the thickness of literature 1 article 3.4.11: buried in the layer of "heating heating pipe material and thickness of choice should be the life of the project requirements, we use the time and the system running the water temperature and pressure conditions determine"; literature 5 6.4.2 stipulates: "the plastic pipes of performance indicators and select calculations, you can reference the Beijing standard low-temperature radiant floor heating technology with the relevant provisions of the Statute of the radiator heating systems using the condition rating selection, should be not less than 5-level requirements"; 4.3.4 literature 6 stipulates: "the heating of materials and wall thickness should be calculated using conditional upon project choose OK, the Select method and calculation data can see Appendix H, I, J,". Appendix H provides heating pipe material and thickness to select calculation method, Appendix I lists the conditions for use of the heating pipes, Appendix J lists PE-X PB pipe, pipe, pp-r pipe of three tubes of allowable stress designed ring D, calculation of σ SCALC.MAX and minimum wall thickness. XPAP (cross-linked aluminum-plastic composite) pipe calculation of the required data is not provided, but because of their allowable stress design ring is greater than the PE-X tube reference PE-X tube to determine its minimum wall thickness required.

Some of the new household heat heating design with a radiator heating systems for the return pipe using aluminum-plastic composite pipe (XPAP), layingIn the cushion, but not for the selection and calculation of pipe wall thickness, drawing on selected only labeled pipe nominal diameter DN20, does not indicate the use condition grading and wall thickness, which is not compliant. Because different using conditions rating, all kinds of plastic pipe to allowable stress design cycles, the pipe wall thickness are different, even if the conditions of use are the same, because the classification of pipe operating pressure, the required pipe materials and wall thickness are different. Therefore, design drawings, not only should mark the selected pipe nominal diameter, but should be annotated using conditional rating and wall thickness. In drawings on the wall thickness according to requirements, designers mark may trouble points, an increase of some artifacts, but facilitates ordering, construction and quality, is totally should.

Plastic pipe diameter dimension can be seamless annotation methods, such as nominal external diameter, wall thickness to the DN20, 2, 2 labeled De20× (De — shown in plastic tubes), the nominal external diameter, wall thickness for DN25 2.5, labeled De25× 2.5.

11, hot fee basis cannot separate heat meter readings household heat metering systems, hot fee should mainly be based on heat meter readings, but a separate charge under heat meter records and heat costs is unreasonable and unjust.

The parts of different households, exterior envelope towards different, area sizes, the formation of larger differences.

The same heating parameters and requirements that are in different households towards the exterior envelope pass heat, heat meter readings vary, most unfavourable to the households in the North, South, to the most beneficial thing households households centered. The same toward, in different parts of the exterior envelope area, the cost of heat radiation, heat meter readings, in the middle layer of household floor, because only a side-wall, heat transfer, thermal load, heat meter reading small; in the bottom of the household, increased floorheat, is in the top level of the households increased roof heat transfer, heat meter readings increase, at the end of the building, opposite the Middle households households has increased by one side wall, heat transfer, heat meter readings increase; you know, these households of floors, roofs, end walls, etc., not only in the household, and service to the entire cell or even whole floor tenants, this part of the excess heat transfer form the exterior envelope of heat load should not only from those parts of the household, but by the whole unit, the whole floor tenants share the responsibility.

Since this portion of the calories is not possible to separate measurement, it can only be used by the appropriate proportion of the approach for processing.

Household heat metering heating system, heating fee is a very complex, policy strong, most can be charged by heat meter records, a substantial portion should be assessed by the members. What is assessed by percentage, you should consider many factors, in addition to the sites of different households, there are some intermittent heating users use or more substantial adjustment temperature caused by another part of the user to increase the heat transfer across, and so on, require careful analysis, calculation, demonstration and research. National and local research should be conducted significant research and careful work, depending on the situation, implementing measures introduced thermal charges and rules for any conditions that make clear, reasonable, detailed requirements, minimize heat fee work do scientific, reasonable and fair.